Life Battery from Leopard Power for your radio box 6.6 volts 1700mAh. It is only 3-1/2" long 3/4" wide and 1/2" tall and will fit nicely in most radio boxes. It is lightweight, high energy density battery with more power than NiCd and NiMH receiver batteries provide and at 6.6 volts there is no need for a voltage reducer like the lipo batteries. We have been using these in all of our boats for almost five years and we absolutely love them. Check around and I don't think you will find this strong of a battery (1700 mAh) in this size for this price anywhere.
LIFE 1800 mAh
2S 6.6 volts
Standard Connector and Balance plug included