pacopaco

There is a CMOS battery apparently, maybe these links will help you

https://www.youtube.com/watch?v=7FolN2rj-ss

At 3:30, in the left-above of the video , i see a circle which seems to be a battery

try to do like this guy in this other video :

Good luck to make your computer starts

it depends on what your computer activities are.

if you do only some text edition, it will be a bad idea

You will not gain that's much, by that i mean that you will not notice improvements without an appropriate tool. Except if you are an hardcore gamer who search for these little fps gain :3