Well, are you using the recommended battery? They do some in all sizes, shapes, voltages, and amperage. Verify that what you have is what they recommend, then, well, do your best to squeeze it in there. It can be a challenge.

I have a couple of smaller foam warbirds. Just trying to fit stuff in the very small compartment AND, try to close the lid.. well, someone gets it right because they fly them all the time...

CGr.