I was very careful. At home, I keep it sitting on a 12" x 12" ceramic tile, sitting on a metal wire rack. It is only plugged in when I am charging and only charging when I'm in the house. I have been monitoring it while charging, feeling it for heat. On this incident, I had the charger sitting on a concrete floor, well away from anything flammable. I had just started the two batteries charging and had gone into the next room to eat dinner. Maybe ten minutes had elapsed when I smelled the burning plastic. Not sure how much more cautious or 'aware' I could have been. I plugged it in, placed two batteries in the slot, the lights indicate it's charging them, I go into the next room, ten minutes later I smell it, go back into the room with the charger, unplug it, remove the melted battery, then the second battery. Short of me holding it in my lap or having a heat sensor with audio alert pointed at the charger, what else can you do? Obvious answer is to no longer trust that brand of charger.
