Unfortunately, but I am unsure even if removing the battery might help, as it is possible that your GamePad has become defective in some way and will now need to be repaired, sorry.
So probably the best thing to do is give a call to Nintendo's 1-800-255-3700 (6 am ~ 7 pm Pacific, everyday) Customer Service number, and one of the service representatives can do some over the phone troubleshooting to determine exactly what the problem(s) might be, and if need be, set up the repair process for you.