The Nuprol Power 8.4v 1600mAh NiMH Tamiya battery is a popular Nickel Metal Hydride battery pack for airsoft guns, featuring 7 cells, a Small Tamiya connector, and a reliable 1600mAh capacity, commonly available in "stick" or "nunchuck" (crane) configurations, fitting many AEGs with limited space, like AKs, for consistent power in skirmishes. 
Key Features:
Type: NiMH (Nickel Metal Hydride)
Voltage: 8.4V (7 cells at 1.2V each)
Capacity: 1600mAh (provides good run time)
Connector: Small/Mini Tamiya
Configuration: Available as Stick (for AKs, long thin spaces) or Nunchuck/Crane (split pack for M4/M16 stocks)
Use: Ideal for airsoft AEGs, but also suitable for RC cars/boats. 
What it means for you:
Compatibility: The Small Tamiya connector fits many airsoft guns; check your AEG's battery compartment and connector.
Performance: Offers dependable power for typical airsoft games.
Charging: Requires a compatible NiMH charger (don't overcharge or deep-drain for best life).
Fit: Choose stick for AKs or nunchuck for crane-style stocks. 
In essence, it's a standard, reliable, mid-capacity power source for many electric airsoft guns.