How many cycles are on your battery and what is its health? If you're not already doing so, use
iStat Pro (free) or
iStat Menus ($16) to get accurate readings of battery health and cycles and computer uptime, among many other things. A forum member has posted a copy of iStat Pro that has been "tweaked" to enhance compatibility with Mountain Lion. You can download it
here.
For battery, power, or charging issues, you might try
resetting the SMC. (PRAM/NVRAM has nothing to do with these issues. Resetting it will not help.)
The link below should answer most, if not all, of your battery/charging questions. If you haven't already done so, I highly recommend you take the time to read it.