Many cordless power tool brands – Dewalt, Milwaukee, Makita, Bosch, and others, have faster and slower battery chargers.
Shown here is Milwaukee’s M18 Dual Bay Rapid Charger, which charges batteries faster than their standard charger. Their Super Charger can recharge High Output M18 batteries at an even faster rate.
Do fast chargers negatively affect power tool batteries? This is an increasingly common question, and a very good one.
A reader wrote in today, prompting me to think about this again. Mosh wrote:
Does charging my tool battery with a fast charger kill them? My Dewalt fast charger has a built in fan for cooling.
In theory? Yes. In practice? Probably not.
Lithium-ion cordless power tool batteries are prone to wear. Each battery has x-number of charge cycles before it loses y-percent of its initial charge capacity. Once the battery pack holds noticeably less charge than before, or fails completely, it’s due to be replaced.
So, the question isn’t whether a fast charger will damage or “kill” batteries, but whether it will accelerate the wear on that battery.
There are several factors that can shorten a battery’s usable life, with heat perhaps being the most significant.
Charging a battery pack creates heat. Charging a battery pack at a faster rate leads to more heat.
Logically, if faster charging means more heat, then doesn’t faster charging also shorten the life of Li-ion battery packs?
Faster chargers typically feature active cooling that helps batteries shed their heat at a faster rate. Charging rates also typically slow down a bit once a battery reaches higher charge capacity, such as 75-80%.
Most sophisticated chargers also contain thermal sensors and will not charge a hot battery.
As long as the heat is controlled, there’s less chance of accelerated wear.
When Milwaukee’s M18 Super Charger came out, I asked them if their Rapid Chargers and Super Chargers affect the usable lifespan of battery packs.
If you have two battery packs, such as M18 5.0Ah XC, with one recharged on a standard charger and the other on a Rapid Charger, will there be any difference in charge capacities or usable lifespan after 50X/100X/500X use and charge cycles?
Here’s what they said:
No, there won’t be a difference in lifespan of batteries between standard, rapid, and super charger.
Packs outside of High Output have a ‘cap’ where they simply will not charge faster on this charger. That ‘cap’ is comprised of many things, like cell chemistry. The high output packs can handle this faster rate without degrading life due to the chemistry and mechanical design of the cell tech.
It’s possible for faster chargers to accelerate battery wear, but it’s also likely that power tool brands take temperature thresholds into account when designing their faster chargers.
In 2019, when I was at Milwaukee Tool’s headquarters for a new product media event, we were taken to one of their battery labs, and I was given permission to walk around while a product manager went over battery pack design basics.
I won’t go into specifics, but the nature of the equipment in the room indicated a level of Li-ion battery cell and battery pack research I never would have expected from a power tool brand.
A few years earlier, Milwaukee’s battery lab at the time included rows and rows of power tool battery and charger banks that were used to automatically cycle their battery packs, as well as competitors’. They have since moved this lab to a different location, and I have not seen it since.
I would assume at least this level of battery development and characterization sophistication from most major power tool brands today.
Can it be guaranteed that faster charging won’t damage a battery pack? No, I don’t think so.
But, to be frank, I have a bit of faith that power tool brands are careful in their charger designs.
The fact of the matter is that battery packs are still wearable products that will eventually need to be replaced.
For my own use, I weigh present value vs. future costs – I use a fast charger if I need the speed, and a standard charger if or when I don’t.
Hypothetically, if a battery that is always fast-charged gives me 200 charge cycles before it loses capacity, vs. 300 charge cycles for a battery that is always slow-charged, is it worth it?
Do you leave your battery packs fully charged for long periods of time? Do you completely drain your battery packs every time before recharging? There are lots of factors that can accelerate wear.
Unfortunately, answering the question about whether faster charging accelerates battery wear requires significant time and equipment investments.
Brands – or at least Milwaukee Tool – say that no, their faster chargers do not accelerate Li-ion cell degradation.
There are a lot of different cordless power tool brands, a lot of different battery pack sizes, and a lot of different chargers. It’s possible that faster charging can negatively affect some battery packs.
Faster chargers tend to be premium add-ons, or are sometimes included as standard with higher capacity batteries. Some other brands’ fast chargers are their “standard” chargers, with slower chargers being value kit inclusions.
If you’re worried about the potential for heat-related wear, simply don’t use a fast charger unless you need the speed benefits.
I think that this is a valid concern, especially with how much high capacity battery packs cost to replace. But, those pricier higher capacity and higher output battery packs can also handle faster charging rates.
How about an example.
Milwaukee Tool has table that shows how fast their M12 and M18 batteries recharge with different chargers. Their Rapid Charger is faster than their standard charger, and their Super Charger is faster than both when recharging High Output batteries. (This is because High Output batteries have a lower charger density and heating profile during charging.)
On Milwaukee Tool’s 3 tiers of chargers, the fastest that an M18 2.0Ah battery can be charged is 25 minutes. The fastest that an M18 compact 3.0Ah HO battery can be charged is 35 minutes. Their M18 6.0Ah XC battery charges in 64 minutes on a Rapid Charger and 35 minutes on a Super Charger.
A compact 3.0Ah battery is likely built with 21700-sized 3.0Ah Li-ion cells. An 18V or 20V Max compact 3.0Ah battery pack would have (5) of these cells.
18V or 20V Max 6.0Ah batteries are likely built with (10) 21700-sized 3.0Ah cells. (Some brands, such as Makita and Bosch, have 18V 6Ah batteries with 18650 cells.)
Okay, so Milwaukee’s M18 CP3.0Ah and XC6.0Ah batteries are built with similar or even identical 3.0Ah cells.
If a Super Charger can recharge each cell in a CP3.0Ah battery in 35 minutes, why couldn’t it also recharge each cell in a XC6.0Ah battery in the same amount of time? If you double the current across double the number of cells, each cell should create comparable levels of hear, right?
Thermal dissipation is important here. As long as the batteries can shed the heat, why would there be any negative effects from a faster charging rate?
A Milwaukee M18 XC8.0Ah battery is built with (10) 4.0Ah cells, and their HD12.0Ah battery is built with (15) 4.0Ah cells. The Super Charger recharges the 8.0Ah battery in 45 minutes, and the 12.0Ah battery in 60 minutes.
Hypothetically, since each battery has 4.0Ah cells, shouldn’t it be possible to deliver 50% more energy to recharge 50% more Li-ion cells in the same amount of time?
But, the 12Ah battery takes 33% longer to recharge than the 8Ah battery.
This could be due to power limitations, but it likely has more to do with cooling. When you have a 15-cell battery pack, there’s a row of Li-ion cells sandwiched between two others, leading to more complex heat distribution and dissipation profiles.
Maybe I’m overly optimistic, but I like to think that, as part of the design process, brands take into account how fast their batteries can be recharged without added degradation over time.
If we disregard tool brands’ assurances, and we cannot easily test this experimentally, what about anecdotal evidence?
Faster power tool battery chargers have been around for quite a few years now.
Have any of YOU experienced noticeably accelerated power tool battery wear after using fast chargers long-term?