All4Cellular offers the Stitchway 1900mAh Backup Battery for iPod / iPhone $6.12 + $2

[Black]

Winston wrote:
Anyone know how this one charges? Specifically, can you have it connected in line with an iPhone and charge both it and the iPhone at the same time?

USB charger>backup battery>iPhone

or do you have to charge each separately?

Thanks.

- Winston

You can stick one in an iPhone, and another in it, and another in that one, and the connecting cable in that one, and everything will charge.
Oddly though if you leave them that way not charging the whole mess will discharge down to nothing very quickly.