This is the FT2F2100BV2 6.6V 2100mAh LiFe Transmitter Battery.
For use with the Futaba 18SZ, 14SG, 10J, 6K, 6J, 4PV, 4PX/R, 4GRS, 4PKS/SR, 4PL/LS, 7PX, 7XC
6.6V 2100mAh LiFe Transmitter Battery with Balance and Discharge
Compatible charger-constant current/constant voltage balanced
charging system such as the Hobbico LiFeSource Charger, HCAM6375
Nominal Output Voltage: DC6.6V
Nominal Capacity: 2,100mAh
Number of Charge/Discharge Cycles: Approximately 500 (depends on
Charging: 32° to 113°F (0° to 45°C)
Discharging: -4° to 140°F (-20° to 60°C)
Storage: -4° to 77°F (-20° to 25°C
Dimensions: 1.7 x 3.1 x 0.67" (42.5 x 79 x 17mm) approximately
Weight: 3.6oz (101g) approximately
Do not use as a receiver battery.