Lithiun Ion Battery Caution

I had a Sears 20V drill in the factory charger that I had used for a couple of years. My mistake was I had a 30 year old power strip that it was plugged into with no breaker and that was plugged into a regular non GFCI socket straight into the 20 amp panel breaker, so there was basically no protection circuit. The charger overheated and set a stack of papers and old broadcast sheets on fire that were right next to the charger.