Airsoftjunkiez got some Lithium Ion Batteries that you can use with AEGs that require stick batteries or power the electric components such as the FCU for HPA airsoft guns... "HPA batteries will never puff and become unsafe like lipos will that have been either neglected or simply aged over time.

No Memory

HPA batteries can be charged from empty or nearly full without damaging the battery. Even if your battery gets low and your device cannot cycle, the battery is still within is safe operating range and can be charged safely back to 100%.

2x-5x the Capacity

HPA Power batteries can store on average 2-5 times the energy of other airsoft batteries, keeping you in the game longer."