This is the Futaba HT5F1800B 1800mAh 6V NiMH Transmitter Battery for the 14SG, 4PKS, 8J and 6J Transmitters.
One Futaba HT5F1800B 1800mAh 6V NiMH Transmitter Battery with Red 2-Pin Connector and an Instruction Sheet
Charging Rate: 170mA - 15 hours
Dimensions: 1.7 x 0.67 x 3.3" (43.5 x 17 x 84mm)
Weight: 5.8oz (165g)