RE: Where to buy replacement TX battery?
Try powerizer battery packs on ebay. I bought 2x1800mah 8 cell tx packs for 18 bucks! They are great and cheap, no problems. Tested them out on a triton and worked normally and have been using ever since with no problem.
I also got 3 5 cell rx packs for the same 18 bucks or so combined shipping with above and got 5 packs for under 50 bucks. Can't beat that.