Problem with my G36c

[TomRobbo94]

I'm new so bare with me of this sounds stupid but i ran down my battery when i went to airsoft last in feb so i chargedy battery up and tried using my gun today just cos i was bored and it doesnt fire very well

 

when on single fire, it fires but like shots 1-3 fine then when i pull the trigger nothing happens

 

then on full auto it fires in bursts but random amounts and it doesnt always go off when i pull the trigger?

 

its a jg g36c and when i went the first time the fps was too much so i had an uprated gearbox put in and have had no problems. Its a standard battery im using so it maybe that i need a new battery? Cam anyone help me with this