Its an 8.4 volt 900 mah NiMH. Rechargeable Battery pack it came with my a&k m4 s system. I charged my battery for about 4 hours yesterday and I went in my backyard today and only shot for about 45 minutes and my gun stopped working when I took the battery out it was pretty hot I think I need a new battery? And a smart charger. can I upgrade my battery or can my gun only use 8.4 volt batteries??