I've seen that happen with controllers. Usually ones that have been beat up a bit. (Not accusing. Just sayin)
The problems I've seen is either:
- the plastic piece holding the batteries is cracked and not holding the batteries in place properly
-or the connections that touch the batteries are busted.
if you have the USB cord, try using that to see if the controller still works. If it does, its probably one the issues I mentioned. If its still busted, than yea, its most likely defective.