AnkerDirect via Amazon offers its Anker 2nd Gen Astro E5 16,000mAh External Battery, model no. AK-A1208011, for $39.99. Coupon code "ASTROE52" cuts it to $29.99. With free shipping, that's $60 off and the lowest total price we could find. It features PowerIQ Technology, which purports to detect your device to deliver the fastest possible charge.