It is best to use the charger that came with your airgun. Make sure the charger being used is designated for the type of battery you have. Batteries that get hot, meaning they exceed being warm to the touch, should not be charged again with the current charger being used. In general, the battery gets warm to the touch when full, but not hot. If the battery gets hot, it is likely the charger has malfunctioned. To verify, plug in a different battery. If that battery gets hot, remove it immediately and replace the charger.