Need recommendation for a battery with a Switcheasy Rebel case

[cashonly]

I want an add-on battery and still be able to use a switcheasy rebel case. I've heard that some batteries don't stay attached too well and am looking for one that will.

Any suggestions?

[Hawk]

Depends on your battery needs. I bought the IMP500 external battery. it's almost the same height and a little wider than the iPhone, but it's a 5000mah battery. yes, 5000 milli-amp hour battery. You can charge the phone approximately 4 times before the battery will need to be charged.
The battery would connect to the bottom of the phone via a cable with a 30 pin connector, so having the case on is not an issue.