PSA - Don't leave cordless batteries on chargers

NOTW

Notw
Senior User
There have been a couple of fires in my neighborhood in the past few weeks, both originating in the garage. One of them has come back as confirmed from the fire investigation that the cause of the fire was a DeWalt battery charger that was left plugged in with the battery on it. So just a friendly reminder to unplug them after they are charged or I have even seen some people having them on a timer system.
 

bob vaughan

Bob Vaughan
Senior User
When battery drills first became popular there were some real horror stories about malfunctioning chargers. While the reliability has improved over the years, it still isn't 100%.
Good PSA
 

Pop Golden

Pop
Corporate Member
What I came up with is a system were my charges stay plugged up, but there plugged up to a receptacle with a switch for each one and a red Christmas bulb that glows when the switch is on.

Pop
 

sawman101

Bruce Swanson
Corporate Member
Thanks for some very important information and cautions, I'm going out to the shop now and make sure there are no batteries on charge. Chargers draw current even when a battery isn't inserted, so I most often unplug them when not in use--but not always; I'm going to be more cautious after this.
 

Phil S

Board of Directors, President
Phil Soper
Staff member
Corporate Member
It is always a good idea to remove the battery when it is fully charged. Fires typically happen when the internal battery management system fails and let one of the cells charge too high and fire will follow. Note: an 18v battery is actually 5 cells each charged to 3.6 volts

Please note it is also important to remove the battery from the charger when the charger is not plugged in. Leaving a battery in an unpowered charger can allow a small uncontrolled discharge and if one or more of the cells discharges down to below 2 volts, that cell will never charge up again.

One more note: If you are not going to be using the battery for some time, a month or more, it is best to bring the battery down to approx. 60% charge
 

NOTW

Notw
Senior User
I knew someone would have the science behind this, we really have such a vast wealth of knowledge on this site, thank you Phil!
 

tvrgeek

tvrgeek
User
I keep my chargers on power strips so I can power them off and try to remember to pull the batteries. A timer is not a bad idea. Li-Ion are not quite as bad as NiCad, but both can go into runaway. Don't forget your yard machine batteries.

So, with the batteries in series, can't see how it can let one cell overcharge without a failure ( short) in another. I can see charger regulators failing, (some history in Kobalt 40 and 80V as well as the simple wall-wart type for Wally World tools. ) and of course cells shorting, but the charger does not have access individually to each cell.

60%? Why is that? I can see taking off the capacitive charge, but not 40%.
 

Phil S

Board of Directors, President
Phil Soper
Staff member
Corporate Member
I keep my chargers on power strips so I can power them off and try to remember to pull the batteries. A timer is not a bad idea. Li-Ion are not quite as bad as NiCad, but both can go into runaway. Don't forget your yard machine batteries.

So, with the batteries in series, can't see how it can let one cell overcharge without a failure ( short) in another. I can see charger regulators failing, (some history in Kobalt 40 and 80V as well as the simple wall-wart type for Wally World tools. ) and of course cells shorting, but the charger does not have access individually to each cell.

60%? Why is that? I can see taking off the capacitive charge, but not 40%.
Let me see if I can explain a bit more about lithium based battery charging. There are over a dozen types of lithium batteries, the most commonly used in tools are lithium iron phosphate (LIFE), Li-on and Lipo. Each uses a slightly different charge process, that is why it is very important to charge batteries in a matching charger.
Each battery has a circuit inside that monitors temperature, charge current and each individual cell voltage. Using an 18v battery as an example, the charger is going to attempt to charge the 5 cells in series up to 18 volts (actually it is 4.2 volts x 5 cells = 21 volts), if one cell will not accept a charge and holds at 2 volts then the other cells would then charge too high to make up for the lost cell - this must not happen as cells may explode if they get above 4.3 volts. When you get an error code or battery fault light on the charger, it is the battery telling the charger that it is either too hot to charge or there is a dead cell (less than 2 volts) or the charge current is too high most likely due to a shorted cell.
I am not sure why the batteries are best stored at 60%, but it seems all cell manufacturers state the same
Hope this helps
 

jcz

Johnny
Corporate Member
My family went through a house fire 3 years ago. During the investigation one of the 1st questions was “Did you have rechargeable batteries on charge?”
Thankfully I did not and was able to prove it. They dug thru the ashes and found my drop cord fully rolled up and exactly where I told them it would be.
The fire investigator found a couple of battery pack remnants and was able to tell me what brand and voltage drill I used.

It was a horrific time for my family but I learned a lot through the investigations. They determined it was a short in the wiring above the garage. It took a total of 3 different investigations to come to that conclusion. Hell of a time. Don’t wish it on anyone.
 

Mike Wilkins

Mike
Senior User
I have seen folks hook up their chargers to a timer that shuts off shortly after the charge time. Worth looking into.
 

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