Batteries heat up depending on the rate of charge and while it is easy to measure and control to avoid damage from overheating, I don't believe it can be used t

Batteries heat up depending on the rate of charge and while it is easy to measure and control to avoid damage from overheating, I don't believe it can be used to measure the state of charge. Charging at home in a garage would likely be using a much slower (and thus cooler) charging method than a commercial charger, so I don't think the fires are caused by the rate of charge, but perhaps by over-charging potentially worn or damaged / defective cells.