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Technical - Workshop Notes
2023-11  November

2023-11  November

“Don't overcharge Lithium Batteries"

by Gary Pope

This article was prompted by observing recent events of a caravan burning to the ground, due to incorrect lithium battery installation.   And it seems to be occuring far too regularly.   A recent survey at a very large storage facility found that 1 in 7 vans there, were using Lithium Batteries.   So they are growing in popularity.  But the concern is, whether they have been properly installed with isolation units fitted and working, to avoid over-heating.

Then there are the stories of EV's left to burn because the fire is unstoppable.


But what about the humble woodworking tools we all use, with lithium batteries?  What should we be aware of?


What happens when a battery is over-charged?

Let's refer to this extract from  

If neither the charger nor the protection circuit stops the charging process, then more and more energy enters the cell. As a result, the voltage in the cell rises – this is known as over-charging. On the one hand, this is harmful to the battery and bad for its life span. On the other hand, it can pose a safety risk for the user. The excess energy leads to heat generation. “In the worst case, this can lead to a so-called ‘thermal runaway’. This means that the temperature in the cell continues to rise and chemical reactions start from it, which proceed exponentially. These reactions can no longer be stopped,” explains Dr. Jürgen Heydecke. In the case of lithium-batteries, this can lead to the cell opening and possibly burning down. “With lithium-polymer batteries, it should also be noted that gas formation can occur in the cell, which leads to the severe swelling of the cell.” The next step would also be thermal runaway and, thus, burnout.”

Well that was enough to prompt a check out of the specifications for usage of the power tools in the shed.   Fortunately Bosch 18v tools have a 'battery level' check button, showing 1,2,3 LED lights, representing  1/3  2/3  full status.    This fits nicely into the 40-80 rule.

What is the 40-80 battery rule?

Let's refer to:

The 40-80 battery rule suggests keeping the battery State of Charge between 40% to 80%. This is done by charging the battery whenever it reaches 40% charge level. The charger is disconnected when the battery is charged to 80%. Following this rule extends the lifespan of the battery.

There are various discussions out there, some relate to phone batteries, some to vehicles, and some on tools.   There seems to be a concensus about not allowing full discharge, and also, not fully charging.

What about tools at the Club house when closed?

Makes you think, that perhaps a best practice approach, is to only recharge batteries when in attendance, and perhaps only up to 80%.

Insurance company statistics show that:   "lithium-ion battery fires in the home are on the rise, especially in garage areas. Emergency services have a new focus on lithium-ion battery fires, and SES is rolling out new training to educate their volunteers about limiting and preventing these types of fires."      extract from:

There is also the lifespan argument.

let's refer to:

So how do you make your lithium-ion battery last as long as possible? You may have heard you need to do a full charge and discharge when your device is right out of the box—but this doesn’t really matter on modern batteries. What matters most is how you charge your phone or laptop after you’ve started using it.     And the same applies to woodworking tools.

Shallow discharges and recharges are better than full ones, because they put less stress on the battery, so it lasts longer. When your battery is discharging, Battery University recommends that you only let it reach 50 percent before topping it up again. While you’re charging it back up, you should also avoid pushing a lithium-ion battery all the way to 100 percent.

If you do fill your battery all the way up, don’t leave the device plugged in. Instead, follow the shallow discharge and recharge cycle we just mentioned. This isn’t a safety issue: Lithium-ion batteries [SHOULD] have built-in safeguards designed to stop them from exploding if they’re left charging while at maximum capacity. But in the long term, electronics will age faster if they’re constantly plugged in while already charged to 100 percent.


It all comes down to being aware of how well installed, isolated and controlled, your recharging system is, particularly if it is some years of age.    There are more and more Lithium powered devices in our lives these days.  Take a quick read of this article.

Happy and Healthwoodworking with your Battery Powered Tools!                                  

Gary Pope 0408 994 799                      


Spanish Fort homeowner says lithium-ion battery in rechargeable toy caused fire

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