Low FPS VFC Aeg rifle

Hey guys.
Recently purchased a VFC KAC SR16 Carbine from a friend. It came with a Turnigy 7.4v 2S 2000mah li po battery and the gun is only doing 280 fps. Also the li po battery is old and a little puffy. Could this be the reason for its low fps? And what battery should I purchase for this? Thank you

[jsae]

A puffy lithium battery is a very bad state. Unless you can be absolutely sure that the outer wrapping is trapping air, you're looking at a dangerous explosive fire hazard.

Any 7.4 V lithium polymer battery will work as long as you can fit it in your battery compartment. And sometimes folks just wire it in and attach the battery to the outside. We just want to shoot.

Seek out Char or Damage for better help.