ProTek R/C LiFe 4PK Car Transmitter Battery Pack (6.6V/2100mAh)
[PTK-LF-CTXF2100-2S]

ProTek R/C LiFe 4PK Car Transmitter Battery Pack (6.6V/2100mAh)
Jake - Rating: 5 of 5 Stars! Verified Owner Saturday, January 26, 2013
I a using it in my radiopost ts401 since there bigbang life is no longer being made. It fits perfectly, same size as stock battery. Just make sure to change low voltage cutoff