All4Cellular offers the Stitchway 1900mAh Backup Battery for Apple iPhone / iPod
, model no. CHEX-ALL-BK-08-319, for $4.99
with free shipping
. That's the lowest total price we could find by $1. (We listed it for 50 cents less in June.) It's compatible with the iPhone 4/4S and 4th generation iPod Touch, as well as other models.