battery problem

[midnight_sailor]

So I've been getting gearbox lockups very frequently lately, and after making sure it wasn't a motor problem, I've come down to the battery as the source of the problem. It's an 8.4v 2000 mah nimh elite battery, and after a full charge it runs the gearbox fine. After a day though, it can only run it for a few shots before it locks up. Is this discharge rate normal for nimh's, or is my battery dying? If it is and I have to get a new battery, what's the largest stick battery with the largest mah that can fit in an ak?