Here’s a question that actually comes up quite often: “what does Ah mean?” When talking about cordless power tool battery packs there are a number of important specifications to keep in mind, but it mainly comes down to voltage and capacity.
Amperes and Amp-Hours
Ah is an abbreviation for ampere-hour, or amp-hour. This describes the charge capacity of a battery, or how much current can be delivered at a constant rate as the battery is depleted over the course of one hour.
For example, consider a hypothetical cordless power tool that continuously draws 1.0A of current. At this rate, it will completely drain a 1.0 Ah battery pack in one hour (under ideal conditions).
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This means that a 2.0Ah battery pack can power the same tool for longer than a 1.0Ah battery pack can, assuming the current flow remains at 1.0A and there are no other differences.
So, a 4.0Ah battery pack lasts twice as long as a 2.0Ah battery pack, right? Sometimes, yes. Other times, no. Sometimes it can deliver more than double the runtime, but this depends on how the battery packs are designed.
Series vs. Parallel
Batteries connected in series are conductively coupled end-to-end. Take two 1.5V AA batteries and attached them so the positive terminal of one is connected to the negative terminal of the other. The voltage measurements taken across the connected batteries should read as 3.0V.
Batteries connected in parallel are connected side by side. Take those same two 1.5V AA batteries and cross a piece of copper across both positive terminals and then another piece across both negative terminals. The voltage will still be 1.5V but they will last twice as long when powering a device.
Today’s 10.8V and 18V battery packs, also called 12V Max and 20V Max in the US, are built with 3.6V lithium-ion cells. 10.8V/12V Max battery packs are built with three cells each, and 18V/20V Max packs have five cells each.
A high-capacity battery pack, such as a 3.0Ah or 4.0Ah 18V pack, has double the number of battery cells as 1.5Ah and 2.0Ah packs. A 2.0Ah battery pack will have five 3.6V cells – each with 2.0Ah capacity – connected in series, and a 4.0Ah pack will have two sets of five batteries connected in parallel.
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P-P-P-P-POWER
But what could it generate? If my math is right, and it always is, 3 gigajoules per second. That could run your heart for 50 lifetimes. Or something big for 15 minutes.
(Scientist Dr. Ho Yinsen and Tony Stark, Iron Man, 2008.)
Power tool battery packs are not so simple where 4.0Ah = 2.0Ah times two. Yes, a 4.0Ah battery pack has twice as many battery cells as a 2.0Ah pack, but the circuitry and controls are usually different.
This is how Milwaukee’s RedLithium higher capacity (XC) lithium ion battery packs can deliver a performance boost over compact battery packs, and why Makita’s heavier duty LXT tools must be powered by high capacity battery packs and not their compact ones.
It’s not just about runtime. Higher capacity battery packs can deliver power via additional channels. Li-ion batteries can be damaged by overdrawing current from them, so modern battery packs have safety measures in place. If a tool wants to draw more current than it should, control circuitry will shut the tool off until it cools down or the load is reduced.
If you have twice as many cells to draw current from, there’s going to be greater headroom.
Let’s say a 2.0Ah battery pack is limited such that continuous current flow cannot exceed 1.0A in order to protect the cells. Theoretically, a 4.0Ah battery pack could be designed where each grouping of cells are set to deliver a maximum continuous current of 1.0Ah. With the two groupings coupled together in parallel, the battery pack could then support a maximum current draw of 2.0A.
But you’re not going to see battery packs advertised as delivering 100% more power than smaller same-voltage packs. Ignoring real-world engineering limitations that govern battery pack designs (such as heat buildup), power tools are not designed to be able to handle 100% more power.
Realistically, if a compact battery pack has a maximum continuous current draw of 1.0A, a higher performing extended capacity battery pack might be designed where it can support a maximum current draw of 1.2A or so. These numbers are all for example purposes. Realistic shut-off limits are likely quite a bit higher.
If a power tool doesn’t draw the extra power extended capacity packs can provide, total runtime is further extended. Since battery cells in parallel share the total load, losses (such as those due to heating) could be reduced. Thus, greater efficiency could enable double-capacity battery packs to deliver more than double the runtime.
4.0Ah vs. 3.0Ah and 2.0Ah vs. 1.5Ah
I discussed this a bit before, but it’s worth another mention. Lithium-ion battery technology has advanced to where battery cell manufacturers can build same-size cells with greater charge density and better performance.
Most of the tool brands I’ve spoken to don’t make their own battery cells, they source them from elsewhere. Panasonic is one that does their own thing, hence their new 4.2Ah battery packs.
Basically power tool brands can – and please someone correct me if I’m wrong – swap in higher capacity cells for lower capacity ones in current battery packs. Change battery cell suppliers or select a different line and whoosh 1.5Ah packs become 2.0Ah and 3.0Ah packs become 4.0Ah. But of course it’s not this simple.
The latest generation of higher capacity battery cells perform better and last longer. But research costs and potentially more complex manufacturing means higher costs for power tool manufacturers and end users.
Some manufacturers are simply building higher capacity battery packs, others are taking the opportunity to incorporate additional changes to power delivery and control circuity. So even if different brands use the exact same battery cells, there will be differences in battery packs.
Summary
Ah is simply a measure of the total charge capacity of a battery pack. Higher values can mean longer runtime AND additional power. Power tools, at least those compatible with both compact and high capacity battery packs, are designed with a current draw ceiling, so you typically won’t see double the power if you pair them with beefier battery packs.
Michael Quinlan
Nice topic, but you’re mixing terms. Amperes is a measure of current flow – it measures electrical charge passing a point during a period of time. Amp-hours is a measure of current flow maintained for a period of time. Batteries are rated in amp-hours. Amps per hour would measure rate of change in current flow (an acceleration), much like the speed of a falling object changes due to gravity. Anywhere you’ve used “amps per hour” in the article, it should simply read “amps”.
Stuart
You’re right. The last paragraph under the p-p-p-p-power heading was especially awkwardly worded so I rewrote it differently. My intent was to convey total power consumption in one hour and not amps/hour, but using “amps per hour” is still incorrect regardless of intent.
Thanks for the comment and nudge for clarification!
Rob Byers
Your response to Michael Quinlan is excellent. Some may have taken offence to being corrected, I thought you did a very good job of ” dumbing down” the information for those of us that would like to know the answer but do not have either one of your electrical knowledge backgrounds, Thank you.
Kris
I’m with Rob. Great response to being nudged a little. Definitely found it informative amps/hr or not. I’m one that would rather be corrected as well. Great read!
KrisR
I’m with them also you took that like a gent, big respect to you
ROB
CAN I USE A 2.0 AH BATTERY IN A DRILL THAT ORIGINALLY CAME WITH 1.5 AH?
THE 1.5 AH BATTERIES ARE DISCONTINUED…
Stuart
Same brand and battery platform? Unless you’re leaving out crucial information, yes, it should work.
Please don’t write with all-caps, it makes things hard to read.
wizbang_fl
amp hours are an average use, amp is a rated as a cap of use. This comes up if you were on a traditional meter and were moved to a smart meter where the smart meter is rated in ah but your home breaker board is rated in amps. The old 15 amp breaker board won’t throw your service. But when converted to ah the rating is a lower value (say 12) So if you draw 14 the utility will kick you off the service for your home (or brown out) damaging your items. I fought with the utility and finally threatened them with a public civil action if they didn’t fix the problem with my service and replace the damage their change resulted in. (they changed the service to an amp hr rating saying the value was the same as the amp rating (a number that was 18% lower than the AMP service I had before) but referred to it in the documents as “the meter will not change your service” When I started to explain how it did they changed their tune and fixed everything. I just couldn’t publicly say the utility name.
Bowick
All house meters measure watts not amps. Amps are part of the equation .
Phil
Actually, there’s no difference in power between a pack made up of five sets of two cells in parallel or two sets of five series connected cells in parallel. Power is an additive function, and since the same number of cells are arranged to have an 18 volt output in either configuration, the ampere-hours as well as the watt-hours are the same.
I’ve had all of my LiIon power tool packs apart at one time or another, in my case they are DeWalt, Milwaukee M18 and Makita high capacity packs, and in each one, the cells are in a 2-parallel five series configuration. Because LiIon chemistry requires individual cell monitoring to prevent dangerous cell charge reversals, deep discharge and charging overvoltage, each pair of cells is individually monitored by the charger and tool electronics to prevent these conditions. If the cells were wired in two sets of five in series, it would double the required cell monitoring nodes since each cell is fully independent of each other. In the 2P5S configuration, the paired cells act as one double-capacity cell, with their voltages locked together. This is a “safer” configuration of LiIon cells as it sets up a sort of “buddy system” where the cells can double their work yet remain at equal voltage during discharging or charging. If the cells are asked to provide 2amps of current, each one ideally will provide one amp each. Of course, the world is not perfect, so there will be sme mismatching. Any mismatching will be seen as that pair of cells being outside the average voltages of the remaining sets, and can be caught by the cell equalization/protection circuits. There are also strict controls on cell temperature extremes when charging and discharging, this also happens with all LiIon packs
Milwaukee came up with the cool idea to allow the tool to draw more power from the pack if the pack is a high capacity pack. The tool “knows” if a higher amp-hour pack is attached and can now “overclock” the motor operation and deliver more power. In actuality, the motor throttles back when a small pack is attached, and runs all out with the large pack. The brushless motor controller has the intelligence to make this work well. In the case of “brushed” tools by Milwaukee (and others) the tool and/or cell electronics can signal when too much power is being drawn from the battery and shut down or cut back on the power draw. The bigger batteries won’t let that occur as much as the small ones, of course.
The DeWalt 18V “XRP” stem-type retrofit batteries have all this smarts built into the cell, since the original tools had no such overload protection. The same 2P5S config resides in the pack, and the “stem” actually has several small circuit boards inside that prevent the pack from being overloaded as well as handle the cell balancing and other duties.. The charger works with that module and regulates proper charging. This is why the old NiCd chargers won’t work with the LiIon packs, the module in the pack can’t control the charging process and prevents it from happening. The yellow LiIon chargers communicate with the LiIon packs, the charger goes “dumb” when a NiCd pack is inserted and uses the common dV/dT charge method as well as keeps tabs on the temperature via the built in thermistor.
Stuart
Thank you for the additional info! I was unaware that 2-parallel 5 series was the preferred way to group the Li-ion cells.
It also makes sense that power tools run “underclocked” when paired with compact batteries and full power when paired with higher performing extended capacity packs.
Michael Quinlan
Thanks. As a former DeWalt tool owner, one of the things that bugged me was DeWalt’s lack of an adapter to me use the new slide-type lithium-ion packs with my older stem-type tools. To the uninformed, this seems like a move designed to force users into choosing between investing more money in stem-type tools and batteries, or abandoning their existing tools and batteries and spending a fat wad of cash on new stuff. If DeWalt had communicated the technical limitations to users, they might not have been so disgruntled.
I would like to see Milwaukee (and others) better communicate the power advantage of extended battery packs too. If you read the specs on Milwaukee’s compact vs extended battery kits, you’ll see a difference, but a lot of people probably don’t notice, as they’ve been conditioned to associate extended battery packs solely with additional run time.
Stuart
Dewalt isn’t alone in doing this – Bosch, Milwaukee, and other brands switched form factors when they moved to Li-ion as well.
Milwaukee’s sell sheets and marketing materials boast the performance boost their XC batteries can provide. To emphasize it even more might confuse users and buyers.
Gillian perkins
I have a matrix 20v cordless leaf blower. Only need to use for 20 min max .Will a 5 ah be sufficient. Is there a generic or compatible brand equivalent to Matrix
matt
I dont think a manufacture can just up the capacity on a pack by swapping cells. In most cases a higher Ah cell will be larger and since they are all limited by the pack they use the space for a larger cell is probably not a option..
Now that does not mean as battery tech improves that you wont get more Ah in the same size cell. I suspect we will keep seeing Ah go up and packs stay the same size as time goes on. I guess my point would be a manufacture will cram as much “juice” in a pack at the time of manufacture as possible..
Stuart
That’s the beauty of the latest generation of Li-ion cells – same size, improved power density. In some cases the chemistry provides improved performance as well, such as cold-weather handling.
That does not mean that manufacturers are simply swapping cells; many are taking advantage of this opportunity to apply additional engineering improvements to their battery packs as well.
New and upcoming 4.0Ah battery packs are said to be the same size and weight as 3.0Ah packs.
An
Thanks for the good info, including from guys in the comment section. I have a Milwaukee M12 Fuel Drill/Driver and have always used the small compact batteries and not the XC because I liked the smaller size. One day I decided to try out the XC battery that came with my kit. I did an A&B test between both the compact and XC batteries fully charged and I noticed the RPM seemed a little higher on the XC. The takeoff or initial RPM seemed the same, but when it reaches fully speed (with the trigger fully depressed) you can hear the higher whine and speed using the XC battery. I believe when using the XC batteries, you be able to achieve your maximum advertised torque too.
Lewis
Can I use a 1.3ah 18v battery with any body even if it came with 4.0ah 18v battery?
Stuart
Depends on the brand.
Makita? Nope, at least for many/most tools.
Bosch, Dewalt, Milwaukee, and most other brands? Yes. Although you will sometimes see a drop in performance.
Ghassan
Thanks very helpful.
Grant
what about the other way around? Would you be doing damage to a skin using a 3.0 Ah battery pack in a 2.0 Ah tool, or would the run time simply be longer with no harm?
Woodwind
Someone should write to the editor of fine homebuilding regarding this. They just ran (Jan 2016) an issue with a shoot out of combos and makita and Milwaukee won, with 4ah batteries against others with 2ah. One of the others being the Bosch ids182 that I just but and is in the mail, but that I hear runs as described in these comments–under clocked-with a 2ah battery and performance massively improves with a 4ah+ battery. Dewalt was also in this test with 2ah batteries. The author just averaged the scores based on screws driven per amp hour but I guess unaware that 50% of his test impacts were running at a handicap. That being said, why isn’t this popular knowledge written in bold if they are going to supply 2ah batteries with kits?! Makita and Milwaukee no doubt picked up a lot of users from this publication, Bosch and Dewalt, whom I both love, need to wake up and get back in the ring!
Stuart
I know that Milwaukee’s M18 drills and drivers, Fuel included, receive a 10% boost in power or so when paired with an XC battery pack compared with when using a compact battery.
I have not yet heard official word (or even user feedback) about other brands’ drills or drivers behaving in the same way.
adam
The bigger problem I have with that FB article, is they are using Gen1 Fuel for testing. Those were known about way back when Stuart went to that Milwaukee new tool show. You can’t tell me that there was no one at FB that didn’t go to that, or at least know or read about it. There wasn’t even a foot note saying a new model is now out. I think that is very disingenuous testing (not using what Milwaukee would send you to test), or at least an article without all the right facts.
Jeff
Hi,
Can someone tell me if a cordless power tool battery has 5.0 ah does it have more power/torque than a battery of 1.5ah?
Stuart
Depends on the brand and tool.
Milwaukee M18 drills or drivers? Yes. Most others, the main benefit is in longer runtime.
Jeff
DeWalt 18v Impact drivers or combi drills
Stuart
I don’t believe so.
Jim
Hi
very interesting post. I am considering buying a DeWalt 18 volt impact driver DCF886 bare unit and was hoping to use the batteries from my drill driver which has 1.3AH liion batteries. Do you know if this will work?
Stuart
If they’re 20V Max or 18V XR slide-style Li-ion battery packs, they should work.
Jason
Man… I was following along pretty good and thought I even had a good understanding of the differences. That is until I started reading the comments. I’m so lost now, I’m taking my new Dewalt 20v Max – 4 Tool Combo Set back and buying me a corded drill. They never lose power and run like a scalded dog all day long. Hahaha. Jk.
ang med
My question… Can I use a Dewalt 20V DCD985 drill with a battery from a
Dewalt DCD741 20V Lithium Ion, ?? Certainly, if it does, the drill won’t run very long.. Am I safe using that combination????
ang med
Sorry, meant to say CDC985 20V
Stuart
I can’t find any product by DCD741 or CDC985.
The Dewalt DCD985 will work with all Dewalt 20V Max Li-ion battery packs.
ang med
Stuart, good show, thanks, man…….Feeling better here now.
Marc
I’m planning on buying the Bosch idh 182. Options are either 2.0 or 4.0 batteries. I’m a homeowner that does some demanding work but no pro. I don’t want to miss out on torque. Which battery should I get?
Stuart
I don’t think you see a torque advantage with Bosch tools.
With Milwaukee, you do see a ~10% peak performance difference whether using a drill with compact or XC battery packs. I don’t know of any other brand that this is or might be true for.
Marc
Thanks so much for the reply. I’m going to get the 2.0 batteries. Even if it did have a slight boost like the Milkwaukee, it’s not enough for the size/weight….and longer charging time of the 4.0. If I was a contactor I’d definitely get the 4.0. Thanks again, take care.
James
Hi, so what I’m gathering here is that I can use the 1.5 ah 20v battery from my edger in my hedge trimmer, which has a 2.0 ah 20v battery, and vice versa? Would I see a significant performance decline in the hedge trimmer (which used the 2.0)? These are Black + Decker.
I’ve just bought the edger and can still return it. The key point for me buying it was so that I could use the batteries interchangeably, since I will never use them at the same time if one battery dies I have the other, and if they both die I can just buy one replacement.
Stuart
Yes, you should be able to. You’ll see shorter runtime, but performance should be the same.
James
Thanks, that very helpful.
Kevin
I’d like to know what would be a good tool suggestion for a Bosch 18v 3ah battery? I picked up one at a yard sale and would like to find the right tool to make the best use of its purpose.
Kevin
Sorry I ment Makita not Bosch
Steve
I’m planning to buy hedge trimmer either DEWALT-DCHT820P1 comes with 5.0 ah battery or DEWALT-DCHT820B bare tool but I’ll spend addition $99 for pack of 3.0 ah two-batteries. Which one is benefit for me if 5.0 ah and 3.0 ah not really impact torque performance but only the runtime? Thanks.
matt
Hi i have a snap on hammer/drill and a 1/2″ impact wrench and the battery cells need replacing. I hav 3ah batteries with 10 18650b cells and wanted to replace with Bosch 6ah cells if possible. Can anyone tell me what cells are in the bosch 6ah batteries?
Mark
So, should I get a 2ah or 4ah battery for my new GreenWorks GBL30800 blower? Thanks.
Stuart
Do you want to save weight? 2 Ah. Do you want longer runtime without having to change batteries? 4Ah.
Chris
Hi! I’ve read all of this and still not clear: how long should I expect my 18v 5ah battery to last in continuous use? it’s in use in a garden leaf blower – it certainly isn’t lasting 5 hours, it struggles to achieve 1 hour of continuous use. I’m thinking of expanding to other cordless tools and not wanting to have unrealistic expectations. Thanks
Stuart
A 1 amp-hour battery will give you 1 hour of runtime at a 1 amp load, or 1/2 an hour of runtime at a 2 amp load.
Similarly, a 5 amp-hour battery will give you 5 hours of runtime at a 1 amp load. With a 5 amp draw, that 5Ah battery will give you an hour of runtime. A 1Ah battery will give you 12 minutes of runtime under that same 5Ah load (under simplified conditions).
Higher power tools will go through battery charge quicker. A leaf blower, for instance, will drain a battery faster than a low power LED worklight would.
Think of it this way – amp-hours are like gasoline in a tank. 10 gallons in one car might give you a range of 200 miles, another car 300 miles, and another 120.
Or consider food. A 250 calorie snack or meal might keep you going from lunch until dinner. For an athlete, that might only fuel them through their warm-up routine.
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BEST REPLY SO FAR I HAVE SEEN EXPLAINED PERFECTLY
Ariel
Will a DeWalt DCD771 20v drill kit with two batteries interchange with the DCF883 20v impact driver without ruining or “killing” the drills batteries completely?
Stuart
Yes, it should, but the batteries that come with the DCD771 are lower capacity than those the DCF883 usually comes with. You will see short runtimes, and you *might* see a slight drop in performance (but I don’t think so).
VM
Adding little more information to the knowledge base here :
– One additional paramter that affects the performance of the tool is the internal resistance of the battery. It’s true that you can regulate current depending on 5S1P ( 5 cells in series) and 5S2P (5S2P) once you identify the battery type i.e. it can affect the performance.
– 5S2P packs obviously will have 1/2 the internal resistance because of parallel combination. When the resistance drops, the internal voltage drop in the batery reduces for the same current draw i.e. more voltage is available for motor.
– Speed of motor is dependent on Voltage and Power of tool, especially impacts will change dramatically based on speed of motor. So it’s on just current but voltage available is also very important especially brushless tools.
– Natually you might see reduced performance with smaller packs i.e. 5S1P even though manufacturers don’t do anything special.
– Higher Ah packs as explained by many above obviosuly gives more run time for the same 5S2P combinations. Cells capacity have increased over years and continue to do so.
– The current draw in most tools especially big impacts can be as high 60A (1/2″ impact), but since these are short bursts, a 5 AH pack would probably last few hundred cycles before discharging. You will see obvious difference as pack discharges too as voltage will drop and speed reduces.
William Kane
Just bought a dewalt 1.5ah cordless drill and I was wondering if I can use a dewalt 4.0 ah battery in it if I bought one thanks
Stuart
Assuming they’re both 20V Max or 18V XR Li-ion packs, yes it should work.
Alan Walters
I want to buy a cordless multi function tool. I already have a dewalt cordless drill with two 1.3Ah batteries. From reading these posts I gather those batteries will do the job although the normal battery for the mft would be 2.0Ah or more. Am I correct?
Stuart
Yes, that’s one tool that will definitely benefit from being paired with higher capacity battery packs.
Steph
Oh my gosh. I’ve read the article and all these posts. Can someone just tell me whether to buy the Black & Decker LST420 (comes with (2) 2 amp-hour battery packs), or the Black & Decker LST400 (comes with (1) 4ah battery pack)?? I don’t need to use batteries at once, so the fact that I would have 2 of one of them is of no value to me. For some reason, the 420 is $30 cheaper. (These are weed trimmers)
Is it worth $30 more dollars to have the 4ah battery?? They’re both 20V.
Stuart
There’s a small possibility that a 4.0Ah battery will last a little longer than 2x 2.0Ah battery packs, but if so, the difference might not be enough to matter.
I’d go for the cheaper set, with 2x 2.0Ah batteries. And if you find that the tool doesn’t last as long as you’d like on 1 or 2 2.0Ah battery packs, you can buy a spare 4.0Ah battery down the road.
I find it more appealing to be the 2.0Ah kit and then a spare 4.0Ah battery if needed, than the higher priced 4.0Ah kit and then 2.0Ah battery if you want the kit to be a little lighter.
Steph
Thank you!!!
John a
I wanto buy a Milwaukee M18BLDD 18v 2×4.0AH pistol drill,but it doesn’t say li-ion after 4.0AH does that mean it atomatically has or not
Stuart
Milwaukee’s M18 4.0Ah batteries are Li-ion.
Emily
So it’s possible to use a new 4.0aH in place of the old 2.0aH the tool came with when I bought it several years ago?
Stuart
For most tools, yes.
Sal
I don’t comment on threads much, but have spent the last hour reading up on MaH in batteries, having just bought a Porter-Cable 20v cordless and looking for an extra battery or two to have as replacements, looking at the knock-off brands versions of the 1.5Mah, 4 Mah, and 5 Mah.
I just wanted to say how great this thread is and say “thanks” to Stuart for being so knowledgeable about all of this. I’m now confident that I can buy the 5mah and use it in my new tools even though the kit came a 4mah battery.
Thanks so much!
Stuart
You’re welcome, glad to help!
You mean Ah. mAh is milli-amp-hour. So for a cordless power tool battery, you would want a 5,000 mAh, or 5Ah battery pack.
Mark H
I really liked the follow up comments in this article as it tallies with an argument I’ve recently been having with someone about the effect of battery pack capacity on tool performance – something which I’m very surprised isn’t more widely understood.
As an electrical engineer can I make the observation that almost any cordless power tool will run more powerfully when used with a higher capacity pack! However, whether you notice that difference is another matter and will vary tremendously between models.
The reason is that whilst a battery pack is specified for a particular terminal voltage (e.g. 10.8V) the actual voltage it provides will drop as the current drawn increases. When you are running a decent power tool flat out you are making a 10A demand (often much higher) on the battery pack. The pack will have an internal impedance (a kind of resistance) which will deprive you of some of those volts. A small capacity pack (<2Ah) could easily have an internal impedance of 200mOhms, which, at 10A would mean that some 2V would disappear at the terminals of the pack. Your 10.8V pack becomes a 8.8V pack!
A higher capacity pack has a lower source impedance. Simply doubling up exactly the same cells by wiring them in parallel would halve the source impedance (now 100mOhms). At the same 10A discharge current now only 1V would be dropped, so your pack now supplies 9.8V. That's quite a voltage difference and, depending on the exact motor characteristics, could translate into an even bigger big power difference. 8.8 to 9.8 is a 11% gain, but if the motor were a purely resistive load then the power available would actually increase by "V squared" and mean a 24% power gain! (In reality most electric motor power cuves are not "V squared" but they do gain power non-linearly with voltage so the end result could be disproportionately higher).
The problem is reduced somewhat with higher voltage packs. First a few lost volts are less significant when you have more volts to start with, and second you need a lower current to produce the same power. However, you are fighting the problem that the higher starting voltage is generated by more cells in series, so you have a higher source impedance.
The bottom line is that I have a suspicion that some of the tools that many people think are designed to "sense" the higher battery pack are actually just running better because they were effectively "capacity constrained" by the smaller pack – and never receiving a decent operating voltage!! This might be especally true for powerful low voltage ones running with small packs.
Carol
Just bought a Ryobi one +18v reciprocating saw with 1.5ah with a j battery and fast charger should I take this back and buy another brand
Mark H
Ryobi make some good kit so I wouldn’t be in a hurry to exchange it. If it does the job you bought it for then why would you need to? My point is that SOME power tools used towards the limit of their performance will feel more powerful when you swap in a higher capacity pack. That’s a general rule of thumb but whether you’ll notice any real world difference will very much depend on the individual product and how you use it. That seems to be the practical experience of others in this comments section.
There are pros and cons with bigger packs. The cons are reasonably obvious but some of the pros are a bit tricky to fully understand.
In general there are many benefits to having as high capacity pack as possible –
(i) the tool might feel more powerful in demanding situations due to the lower impedance (lower voltage drop),
(ii) the run time will be disproportionately longer. A 4Ah pack will typically outlast 2 x 2Ah packs. This is partly because (a) the larger pack should have a lower impedance, so the I2R (I squared R) losses within the pack will be lower. (Smaller packs have to work harder and aren’t as efficient when doing so), and (b) the bigger voltage drop in the smaller pack (point i above) will cause the battery monitoring circuitry to considers the battery is empty sooner. In effect a smaller pack will be unable to deliver the last mAhs in a useful way and the tool will shut down before the full capacity of it is used. (Note that even a large pack shuts down before the last of it’s capacity is used, it will just be a lower %!). FYI I found it interesting looking at a recent deWalt 2.6Ah battery pack advert which claimed this would run 50% longer than their 2Ah pack. 2.6Ah is 30% more, so why claim 50% longer? It’s mainly for these two reasons!
(iii) the pack lifetime (time to replace) will be longer than the equivalent in smaller packs. This is because (a) you are getting a higher % of the used charge out of a bigger pack, so need fewer recharge cycles, and (b) the discharge current relative to the capacity of the pack is higher in a small pack, which is more detrimental to its health. (In other words you have to flog a smaller pack harder for the same performance which will age it more quickly).
Given that you often pay less than 2x the price for 2x the capacity that’s quite a powerful set of arguments – it makes the tool run better, it will last disproportionately longer per charge, have a lifetime disproportionately longer, and it costs less per Ah than smaller packs!
It’s not all positive though LOL. A higher capacity pack may be more than you want to pay. It is also bigger and heavier. Also, having two smaller packs allows you to charge one whilst using the other. Those could be big issues in some applications.
I would always encourage people to buy the biggest capacity packs (tools) that meet their size, weight and budget constraints. (And preferably stay with a range of tools with interchangeable packs). Note also that capacity here is actually the Watt hours (Wh) which is the pack voltage multiplied aby the Ah rating.
In general people think about the motor being the engine in a power tool and the battery tank is just the fuel tank. I think that’s the wrong way to look at it! A much better analogy is that the battery is both the fuel tank AND part of the fuel injection system. It is also an intimate part of the engine which has a big impact on performance, economy and lifetime.
I wouldn’t be in a hurry to rush back and change that Ryobi. It has a 27Wh pack (18 x 1.5) which is better than many 10.8V packs (even a 2.5Ah 10.8V is still only 27Wh) so it definitely has the potential to deliver a decent performance.
RCWARD
All that and these companies still have to make their batteries non compatible with each other just to make our lives that much harder.
Stuart
https://toolguyd.com/why-wont-power-tool-brands-standardize-their-battery-packs/
tiramisu
kudos to mr. Stuart — 5-years running
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SS540
I have a Kobalt 80v blower and I have several 2ah batteries that typically last about 13 minutes each on high speed. I would like to have longer run time even if it means a larger heavier weight battery. About a year ago I saw 80v 4ah batteries for sale but the price was hard to justify. Now I don’t see any 80v 4ah batteries for sale. Did the manufacturer quit making them? I am seeing a few 2.5ah batteries on ebay but I doubt that they would increase run time significantly.
Robert
I drill maple trees for making maple syrup using a 7/16 drill bit what kind of cordless drill should I buy,( voltage and AH battery) for max drill time per charge?
Stuart
How long is the drill bit? What kind of drill bit?
If budget isn’t a concern, I’d say 18V brushless with a 5.0Ah battery pack would be a good start.
Larry
How does a 24Wh 18v ryobi compare to a 3.o Ah ryobi?
Stuart
Volts x Amp-hours = Watt-hours.
18V x ? Ah = 24 Wh.
Ah = 1.3Ah.
3.0Ah will give you a lot more runtime.
thejoetaylor
As did tiramisu, I have to applaud Stuart for still responding to this thread. That is outstanding commitment and dedication!
I happened upon this post because I am tired of my gasoline powered tools (string trimmer, hedge trimmer) dying every two or three years, so I decided to go cordless electric. In my research, I was baffled by the battery options, and why an extra battery costs as much as the initial kit consisting of the tool, the battery and the charger. I guess it’s like razors and razor blades! Anyhow, this post has been most informative and I enjoyed reading the posts of some very smart people when it comes to electricity and batteries. Regardless of which brand I choose, It seems obvious that I should choose the maximum battery pack I can afford (much like RAM in a computer) and physically lift at my age. When it becomes necessary to go with a lighter battery, I can always ‘downgrade’.
Stuart
You’re welcome, and thank you!
One thing to keep in mind is that sometimes upgrading to a higher capacity battery pack can be done without any increase in size or weight.
Things are more complicated these days, though, because bumping up to a higher capacity battery pack can sometimes involve an increase in size and weight. When this post was written, there were 5-cell and 10-cell 18V (or 20V Max) battery packs. 5 cells for compact size and light weight, 10 cells for greater performance and charge capacity.
Cordless outdoor power tools followed similar general patterns.
But now, there are 15-cell 18V-class battery packs, as well as 5-cell, 10-cell, and 15-cell battery packs built using larger Li-ion cells, for greater performance and runtime.
A rewrite or update is perhaps warranted, to help sort through the many more options that are available too.
poconojack
Does increased Ah increase charge time? Will a 5.0 Ah take 5 times longer to charge than a 1.0 Ah?
Stuart
Usually, yes.
William Cochran
Will a dewalt dcf899. Impact wrench benefit from a dewalt battery dcb204 4ah or a dcb609 9ah , looking for more power and run time???
Stuart
More power? I don’t think so, but I haven’t tested it to check.
Greater runtime? Absolutely!
It’s hard to tell when the tool’s feel or balance will be thrown off by the 9Ah battery, as it’s not exactly compact or lightweight.
Greg
I am looking at a Ryobi 18-Volt 4.0 Ah string trimmer vs. a Ryobi 40-Volt 2.6 Ah string trimmer. Do I get more bang with a higher volt or more bang with a higher Ah?
Stuart
Generally, the higher voltage can potentially deliver more power.
Voltage x Amp-hours = Watts-hours
18V x 4.0Ah = 72 watt-hours
40V x 2.6Ah = 104 watt-hours
Ryobi has a 40V 5.0Ah battery, which would give 200 watt-hours.
notinuse
I think you mean energy, not power. Watt-hour is a unit of energy.
Stuart
While you are correct about watt-hours being a unit of energy, I do mean power.
Apples-to-apples, let’s say you have a 36V tool with a 2.5Ah battery, and an 18V tool with a 5.0Ah battery. Energy-wise, both systems have the same 90 watt-hour spec. But chances are, you’ll get more power out of that 36V tool. That’s a completely different discussion, which is why I simplified my answer into a look at watt-hours for determining which system gives the “bigger bang.”
Tom Reed
Thank You for this informative question and response(s). I’ve been scrolling down and finally found the info I was looking for as I, too, was looking at the same brand and voltage/amp models. You have answered my questions and helped me decide which unit to purchase. It looks like the “bigger bang” is the 40v unit.
Mike Parenteau
My B&D GCO1200 drill’s HPB12 battery is dead. It has no Ah markings, but I think it’s a 1.5Ah battery. The battery’s base has 2 metal prongs, which plug into the drill’s 2 female contacts. There’s a ‘replacement’ 2Ah HPB12 battery with THREE metal prongs. Can I use the THREE-prong battery with the drill’s 2 female contacts? The third prong looks like it will just sit in an empty contact-less slot in the drill. I’m asking because the 2Ah replacement batteries are cheaper than the 1.5Ah batteries.
Thanks for any advice.
Stuart
I can’t find enough information online to answer this. Have you contacted Black & Decker for their advice?
Mike Parenteau
Hi Stuart,
Shame on me for not calling Black and Decker first.
I called today; customer service rep said it shouldn’t matter which B&D 12V battery I use, but she didn’t sound too confident. So I’ll try a (cheaper) three-prong 12V 2.0 Amp-hour battery with my two-prong 12v drill and see what happens.
Thanks for your feedback,
Mike P.
Stuart
No worries.
I was really hoping they would have given you a specific model number to look for.
I’m always willing to try to help, but in this case I wasn’t confident enough about the answer.
Here’s the problem – you need a HPB12 battery, which I can’t seem to find anywhere. 3rd party “replacements” might be questionable. (I’d never trust them.)
If it’s a NiMH or NiCad battery pack, there are some places that can rebuild it with fresh cells.
If the HPB12 has been replaced, what can work in its place? That’s the question I was hoping B&D could answer for you.
Searching deeper now, I see that Home Depot has a listing for the HPB12, and shows it’s a NiCad battery. They have replacements for $27.62.
Personally I’d rather go with that replacement, OR find a place to replace the cells in the battery before going with a 3rd party replacement.
OR, I’d maybe put the money towards replacing the cordless drill with a new one, if I planned to use it regularly.
Andrew
Thank you for writing this excellent article. I was searching for an explanation of why greater capacity batteries can result in a power tool being more powerful. Your explanation was excellent.
Seeing as this is such a useful article, may I make a tiny contribution. Towards the very beginning of your article, you wrote something that confused me for a while until I got it straight in my head.
“Ah is an abbreviation for ampere-hour, or amp-hour. This the total amount of charge a battery can deliver in one hour.”
I don’t know if I can explain what the problem with this sentence is, but I will give it a go.
You should actually stop the sentence at “This is the total amount of charge a battery can deliver.” By writing “in one hour” you have made the Ah into a “rate”.
Current (Amps) is a measure of the rate of flow of electrical charge, in other words Charge/Time. So an AmpHour is (Charge/Time)xTime, which is Charge.
I don’t really think that explanation was necessary because you demonstrate, from what you write immediately after, that you understand what an AmpHour is, so I think it was just a sort of thought-typo.
Stuart
Thank you, I appreciate it.
I can agree that it’s not the smoothest phrasing. I reworded it, and will take a fresh look to see if anything else needs polishing.
Shaun
What is best to use in a cordless circular saw 18v 5.0 ah or 24v 3.3ah ?
Stuart
I’m sorry, but that’s not enough information for me to answer one way or the other.
Darcy
I am curious about the flex volt system by Dewalt and being a contractor battery longevity is just as important as power as I work in remote areas so the less I bring the better
Bill
I fell heir to an ENERGUP Lithium Ion 18V Max LB4018 18v 4.0ah 72W Battery (what a lot of numbers etc???) . It has 4 connections to fit to charger or user unit. Will this charger do the job…Charger For Porter Cable/Black+Decker 20V Battery PCC692L PCC691L PC18B PC18BLX Ebay No: 124010925250 (EBAY UK)? Also, obviously I will need to get the user unit (s) drill or whatever to be compatible…..any idea which makes they may be. – What a “jungle” this is????
Richard Armstrong
Hello
I am looking to replace my De Walt DE 9098 1.3Ah battery. I had 2 originally but the first lasted no time at all and so have been using the remaining battery alone which is a real pain to have to keep stopping to recharge. It seems from your earlier advice that a replacement battery (not a De Walt ) with a 3.0Ah would be fine but my question is can I use the same existing De Walt charger on a non De walt product with a different Ah?
Many thanks in advance for your kind help.
Stuart
You should be able to charge any Dewalt 20V Max battery in any Dewalt 20V Max charger.
Richard Armstrong
Thank you Stuart but will my existing De Walt charger also charge a non De Walt replacement battery ?
Many thanks
Richard
Stuart
Sorry, I have never tried off-brand replacement batteries before. It could work, but I really don’t know.
Richard Armstrong
Thanks anyway Stuart
Best wishes
Santosh
I have a Stalwart 18V 1.5AH LI-CD battery. I lost the adapter for the battery charger and looking to source a new one.
Could you please advice what type of adapter I need to get.
Regards
Santosh
Stuart
I can’t quickly find one online. Have you tried contacting the manufacturer or retailer?
Dom
Can I use a Makita 18V 6.0Ah Lithium-Ion Battery with a Makita 18V 5.0Ah Lithium-Ion Battery (at the same time) for a 36V power tool such as a Makita cordless lawn mower? I already own a Makita dual charger station with 2x 5.0Ah charger packs but have been given an extra 6.0 Ah battery pack as a gift.
Regards,
Dom
Big Richard
Yes, but the runtime will be based on the smallest battery used, in this case the 5Ah. Once the 5Ah battery is dead, the tool will no longer run, despite there still being some charge left on the 6Ah battery.
So adding in that 6Ah battery will not extend your runtime. You would need to run two (2) 6Ah batteries to get extra runtime.
Stuart
Agreed.
Sorry Dom – I must have missed your question.
Ryan
Too bad I don’t understand anything in that article. I just purchased a compact or portable radio/bluetooth unit to use for an ipod. I didn’t pay attention that batteries and chargers are sold separately. The brand is Bauer. All batteries are showing to be 20v but different Ah amounts. They range from I think 1.0 or 1 5 up to 5.0 i think was the highest i saw. From the article, do the Ah numbers mean they don’t last longer than about 2 hours before needing charged?
Stuart
Consider 1 cup of water. How long it lasts will depend on how thirsty you are – that will depend on the circumstances. Now consider a 1.5 cup bottle of water, up to 5 cups. The more water, the longer you can drink for without going for a refill. It also means that refilling the container will take more time.
Ryan
I was out walking just now and started thinking about it. Maybe if I worded it differently. The examples of how it all works only mentioned how much power moves for one hour. I need about 8 hours of power.
Tom D
You have to figure out the “run time” per Ah – if the radio were a bucket, the “current drain” would be the hole in the bucket, and the “run time” would be how long it would take for a given amount of water to drain out.
ALL ELSE being the same, a 2.0 Ah batter should last twice as long as a 1.0 Ah, and a 5.0 Ah five times as long as a 1.0 Ah.
I usually try to get the largest battery I can, unless weight is an issue.
That one they recommend the 3.0 Ah battery for “30 hours” of play (I think) – this would be lower if you’re using Bluetooth and/or charging a phone.
Ryan
Ok thanks. It would be primarily for playing an ipod. I guess the highest number, such as a 5.0 would be best, depending on how loud I would need the volume to be. But then the price….. 🙂
Gerry
Hi, great info and informative comments, can I ask & hopefully not a stupid question, if I have a power too;, such as an impact driver, will a higher Ah battery give me more/better torque than one that is of a lower Ah.
Thanks Gerry.
Stuart
Depends on the brand, but generally, no.
For a tool like that, a higher amp-hour batter generally only provides for longer runtime.
Robert K Courtis
i have a question. i have a cordless drive with an 18v 1.5amp hour battery, it came with a compatible charger. i also have a jobsite radio. it has a 18v 3 amp hour battery. can i charge the 3 amp hour battery on the charger that came with the 1.5?
Stuart
Assuming they are the same slide-on shape, then yes.
Shawn
Just passing on some thanks for the article. It’s old but as you’re likely aware – very useful! Thanks again.
Stuart
Thank you very much! I’m glad that you found it helpful!
Dava
I am having trouble finding a Ryobi P102 18V Lithium-Ion High Capacity Battery 1.3Ah 24Wh. What replacement battery would be safe to use?
Dava
I found one on eBay, but the order was canceled by the seller.
Stuart
Any Ryobi 18V One+ battery.
Here are some compact battery SKUs:
1.5Ah: P189
1.5Ah: PBP002 (coming soon)
2.0Ah: P190
2.0Ah 2-pack: P161
2.0Ah: PBP006 (coming soon)
Grahame
Hi guys,
I just need to know if this will be fine for my needs. I have Ryobi Cordless blower CBL1802, I also have a Ryobi Cordless Hedge Trimmer CHT1850. The batteries that came with them were both a Ryobi one+ 18v 24wh Li-Ion Lithium 1.4Ah BPL 1815 (130429009). and are useless even when fully charged. They die after no more than about 2 minutes. So given that they are not very strong and don’t last very long. So going by the comments made so far what battery ah rating would you advise or suggest I could safely use that would be better and last a lot longer as I have a reasonably large area with a number of pathways etc to cover. I’ll probably buy two as a backup. I would greatly appreciate any advice or suggestion given.
Cheers
Grahame.
Stuart
If in your shoes, I would look at the Ryobi 4Ah 2-pack, which is on sale right now as a holiday season special buy for $79. 4Ah should give you a bit more runtime than a 1.5Ah battery, as well as high value for the money.
There are other batteries, including “high performance 4Ah”, but I believe you should see improvement with the standard 4Ah batteries.
Grahame Clarke
Ok thanks Stuart that’s greatly appreciated I’ll give it a shot and let you know how it goes.
Cheers.
Grahame
Hi again Stuart,
Well time hasn’t been on my side in the past week and haven’t been able to get around to purchase the batteries that you recommended which I intended to do over the W/E . But just this morning a friend of mine calls me to inform me that unfortunately had a mishap and accidently ran over his Ryobi hedge trimmer with his Ride on mower and destroyed it and now has a Ryobi 18v 5.0ah that he hasn’t had all that long and no longer requires it at this stage and I’m welcome to it if I can put it to good use. So what do you think would it be ok to use in mine I just thought I’d confirm that with you if that’s ok! I’ll probably still get the ones that you suggested as I’ll need backups.
Cheers.
Stuart
Sounds like a bad day for him, but good news for you.
Try his battery. If you’re happy with the weight of the tool and the runtime the battery gives you, you might not need to buy any others. However, if you have a slow charger, you might still want a second battery or maybe a faster charger.
Grahame
How much difference is there in weight between the two (18v 4.0 & 5.0Ah?
Stuart
I don’t believe I’ve seen a 5Ah here in my region, but there’s a 6Ah that’s physically larger than the 4Ah. I can’t tell if the 5Ah that’s available in some areas is larger than the 4Ah.
In most cases, there’s no size difference, but there has been differences for some brands, such as Ridgid, whose cordless power tools are made by Ryobi’s parent company.
So, I don’t believe there’s a difference, but I can’t be 100% sure, hence the comment. The 4Ah and 5Ah are both definitely larger than 1.5Ah and 2.0Ah batteries.
Archie
I have a 40V 6aH battery powered Ryobi mower and get ver two hours of operations. I’m thinking of buying a chain saw that comes with two 40V 4aH batteries and charger. Based on the comments and explanation I can interchange the batteries.
michael
Do you know anything about Rockwell 5 in 1 . 2x18v Line trimmer kit. Are they any good?
James D
I have a hart electric lawn mower 18 inch lawn mower. I was purchased with a 40 V AH battery. I purchased an extra battery that’s a 40V 5 AH. What is an estimated run time of each under normal conditions?
James D
Stuart
If Hart doesn’t offer runtime expectations for that model, it’s not something I’d be able to tell you. Mower runtimes tend to vary depending on power consumption, battery size, as well as grass height and type.