Difference between 3200mAh and 4200mAh?

I'm going to buy a charger case for my iphone but don't know they difference between 3200mAh and 4200mAh, can anyone explain?

1000mAh.

The cases have an extended use battery on them. The higher the milli amp hour number rating of the battery the longer the battery will last before it needs recharging. So get the 4200 mAh (4.2 Amps) one for longer operating time.