These batteries wear out after around 300 charge/discharge cycles. When they wear out, it's no different from any other kind of rechargable battery. Except they're a whole lot more expensive of course. So what you need to do is go out and buy yourself a new battery. When you get a new battery, you can prolong its life by plugging into the A/C whenever possible, but the more you use a battery, the sooner it wears out.
I have a 2009 MBP and have just recently started having a problem with the battery. I have popup box that appears and says;
"Because a USB device was drawing too much power from your computer, one or more of your USB devices have been disabled."
But there no USB device connected. Also, when I put my laptop to sleep and go back later to use it, the battery is completely drained after no more than an hour or two.
My MBP has 8gb of ram and is running Mountain Lion. This problem has just recently appeared. I have tried a SMC reset, and run an Apple Hardware Test, and nothing is helping so far. Any advice? Thanks.