Matrix High Output 8.4V 5000mAh Ni-Mh Large Type Airsoft Battery Rechargeable Battery Pack.
Specifications:

Power (V): 8.4V
Capacity (Amp): 5000mah
Type (For Airsoft): Large
Dimension: 156mm x 48mm x 23mm
Cell Type: Tenergy. Pack may come in black or clear shrink.

Feature:
- Long Recharge Life cycle.
- Consistent, reliable power output.
- Super high capacity, will last you a whole day of regular play when fully charged.
- Advanced Ni-Mh technology. Easy to charge. Does not require discharging.
- Enhanced ROF (Rate of fire)
- Reliability: All Matrix brand battery packs are factory direct and sold within a few months, you will never risk buying an old battery pack.
- Recommended to be charged using a smart charger.
(The Capacity of this battery is so high, you don't want to wait next to your wall charger for 12 hours risking over charging it or damaging the battery. Always use a smart charger on good batteries. Wall chargers are for the free / cheapo batteries that comes with your AEG for testing purpose.)

Reviews:
This battery pack will last you forever! For an average game play of 2000~3000 rounds a day, this pack can probably last you over 5 days of playing! (And its Ni-Mh, so its easy to charge it full before you go shoot.) Matrix is one of the biggest Airsoft accessory manufacture in the world. Their consistency in providing the most advanced battery technology at great pricing, pretty much guarantees that you get the best stuff and never an old battery pack since everything gets sold within a few months.

Get a smart charger and you will be spoiled from how easy it is to manage your battery.
*Battery pack may be wrapped in black, green or clear wrapping.