My bad I misunderstood. If the guide is correct then a 9.6V battery with a 120 spring should work just fine.
8.4 Volt 600-1000 mAh All stock TM, ICS, and CA products
9.6 Volt 600-3300 mAh All Stock TM, ICS, and CA products as well as Replicas that have been upgrade to around 400 fps
10.8 Volt 1100-3300 mAh Fully upgraded only Replicas that have all reinforced parts, gearboxes, and motors. Commonly used in sniper rifles. We do not recommend using a 10.8 volt battery in most AEG's.
12 Volt 1800-3300 mAh Commonly used in sniper rifles. We do not recommend using a 12 volt