This is the Hitec NiMH 4.8V 750mAh Rx battery pack.
Features: Flat pack with lime green shrink wrap and 22AWG lead wires with a universal connector
Includes: One 4.8V 750mAh flat battery pack
Requires: NiMH compatible charger
Length: 2-1/4 (57mm)
Width: 1-1/8 (28mm)
Height: 1/2 (13mm)
Note: These are AE sized cells.