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Get this TurboJuice Backup Battery Case for iPhone 4 and iPhone 4S for $9.99 from Tiger Direct after using this $15 mail-in rebate. Shipping is around $3.75, depending on zip code. This is the lowest price we found by around $15. The case offers rechargeable back-up power for an iPhone 4/4S. There is no sales tax (except FL, IL, NC, TX, GA, SD and ID).