The battery had been sitting on a wooden table in our house for about two weeks undisturbed since I had charged it. It was sitting inside the house at a maximum of 85 degrees F and out of sunlight. I came home to a house that was so black inside that I couldn't see more than two feet in front of me. My dogs were in the house, but luckily they are acting normal. After the smoke cleared, I found that the battery caught the wooden table on fire. The battery had partially melted onto the floor and splattered on the wall. I also found small copper colored pieces of foil throughout the room. The house is covered in a layer of soot and it smells very bad. The charger was connected to the 40v 4ah battery, but it was unplugged. The battery was at most 2years old and didn't have that many charge cycles on it because I don't use it that much.