differences between droid incredible extended life batteries?

[ak990]

i would like to buy an extended battery for my Droid Incredible. There are a variety of options with different numbers of "mAh". Can someone explain the differences and pros/cons of each? Do some not fit certain cases?

 

[droid6user]

I have two of the regular batteries. It is exactly like the one that came with the phone and it fits no problem. It is also thin enough to fit in a normal cover. Wouldn't you have to carry two covers for two types of batteries?