X5 Mobile via Amazon offers Prime members its X5 Mobile 10400mah External Battery Pack with Dual Charger Port, model no. Y25, in Black or White for $24.95 with free shipping. (Non-Prime members can spend $35 or more to qualify for free shipping; otherwise, shipping adds $5.25.) That's $6 below the lowest total price we could find for a similar battery back. It is capable of charging any device via USB.