The pack is (was) 1800 mAh NiMH, 8 cell. From the looks of the damage, only one cell blew. I don't know if other cells were hot but the entire plastic overwrap melted down all around. The charger is a small one and was set to 1 amp output and claims to have an overcharge protection circuit. The battery was used last in August but I did put a charge into it a couple months ago and have not discharged it since (other than some minor radio and motor testing - 30 sec max of motor run time). If batteries are in storage for more than a couple months should they be discharged before recharging? The charger instructions pretty clearly state that the charger monitors battery charge and will not overcharge. BTW, the battery is only one year old and was used only a dozen times.