Got one of these 1000mah things in mine
http://www.vapextech.co.uk/acatalog/...Batteries.html
works a dream and stays at 6.5v for ages. Plenty to do 3-4 all day events without charging. Turn off Tx even if the 10min warnout alarm goes off if you forget.
Literally cut the female end off this
http://www.maplin.co.uk/servo-extension-lead-48176
Cut the white cable off completely, cut the battery tray out of the Tx and solder the red and black wires on as needed. Job done