This is a replacement E-flite 1S - 3.7V, 25C, 500mAh LiPo Battery Pack.
Specifications:
Type: LiPo
Capacity: 500mAh
Voltage: 3.7V
Weight: 0.51 oz (14.5 g)
Configuration: 1S
Length: 2.35 in (59.5mm)
Width: 0.75 in (19.0mm)
Height: 0.30 in (7.5mm)
Maximum Continuous Discharge: 25C
Maximum Continuous Current: 12.5A