Macbook - Spare battery

I am going to be using my macbook in university and i think it would be a good idea for me to have a spare battery just incase i need one.

1. Where do i get them from and how much are they?

2. How would i go about charging them? would i need to charge one, take it out and put the new one in the macbook then charge that one?

I just got one from apple.com for $130

take a look at this - it may be just what you need
http://www.newertech.com/products/charger_cond.php

EDIT: just noticed the price ($149.95), you might just want to go about doing it the way you've described