Rampage MT receiver problems

[G-Man]

I know this is a kinda necro - I switched to a Futaba receiver, and I was wondering if someone knows of a decent lipo that will fit in the battery box? Or are they all just the wrong shape, and have to be run externally?

I use this lipo. It lasts forever and is smaller than the stock nimh. I use velcro tape to fasten it to the box.