This thread at WoodNet: Fire Starting Battery Charger tells horror story after horror story of houses and workshops burned down because of batteries left to charge over night, unattended.
Don’t do it.
I read through all 5 pages of comments and summarized 8 safety tips you could use to better protect your family, your tools, your livelihood (for some), and oh yeah – yourself. I guess we need to add battery chargers to our top 10 list of most dangerous power tools…
8 Tips for Battery Charging Safety from WoodNetters
1) Don’t leave batteries charging overnight. Ever.
2) Put battery chargers on a switched power strip that also runs your radio (or TV, or something you wouldn’t leave on)
3) Put battery chargers on interval timers – many only take an hour or two to charge fully.
4) Put a smoke detector in your shop/near your power tools.
5) Check to see if your batteries/tool have been recalled. (Search for recalls here >>)
6) Beware when formerly silent chargers start “singing” or whining.
7) Don’t trust the manual if it says it’s ok to leave batteries charging.
8) Have a separate insurance policy for powertool replacement costs.
Fire Starting Battery Charger has excellent discussion, some technical, some heart breaking, and all of it will help your resolve to change your battery charging habits.
Here’s a video of what happens in PC laptop lithium ion battery fires. Temperatures exceed 1,000 degrees (I assume that would be similar in power tools?):