This is the Sanwa LF2-1850 LiFe Transmitter Battery for use with the MT-4, MT-4S, M12 and M12S. This battery features LiFe technology and is equipped as a 6.6V 2S with 1850mAh of capacity. This battery is a great alternative to using "AA" batteries and will offer longer use time and lighter weight, as well as rechargeability.