could of been a wireing problem.
^This. Check the battery in another gun that works. Then check your gun with a different battery. You would also do well to check your gearbox's shimming job, since it's new (not battery related). If this battery is the one that in fact did come with the gun, you should dump that bitch and get a battery from a reliable maker.
Questions for you, as well as for you to think about if you get another battery:
Manufacturer?
Capacity?
Chemistry ( NiCad vs NiMH etc)?
Discharge rate?
Connector type?
What kind of charger are you using on it?
The battery is one of the most important and under-valued upgrades that go into an AEG.