This is the FT2F2100BV2 6.6V 2100mAh LiFe transmitter battery.
Features: For use with the Futaba 18SZ, 14SG, 10J, 6K, 6J, 4PV, 4PX/R, 4GRS, 4PKS/SR and 4PL/LS
Requires: Compatible charger-constant current/constant voltage balanced charging system such as the Hobbico LiFeSource Charger
Nominal Output Voltage: DC6.6V
Nominal Capacity: 2,100mAh
Number of Charge/Discharge Cycles: Approximately 500 (depends on usage)
Dimensions: 1.7 x 3.1 x 0.67 (42.5 x 79 x 17mm) approximately
Weight: 3.6oz (101g) approximately
Note: Do not use as a receiver battery.