The PRAM battery has been eliminated since unibody model introduced. As a result it will be reset and you will lose your computer current date and time once you disconnect the main battery from your computer which automatically resets the PRAM to defaults. So there is no PRAM BATTERY.
Secondly, if you want to make sure if the battery is causing problem, simply reset the SMC by this procedure:
* Shut down the computer.
* Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
* On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
* Release all the keys and the power button at the same time.
* Press the power button to turn on the computer.
When you reset the SMC, the LED on the MagSafe power adapter may change states from orange to green or temporarily turn off. It gonna return to normal in about 5 seconds or less.
Hope it helps and if it did, please rate it. Thanks.