Idealpoint via Amazon offers the New Trent PowerPak+ 12000mAh Portable Xtreme Dual USB Port External Battery Charger, model no. NT120R, for $59.95. Coupon code "NTCHARGE" cuts it to $44. With free shipping, that's the lowest total price we could find by $11. It's compatible with most smartphones and tablets and is able to charge two devices at once.