New Trent Powerpak 11.0 11000mAh Dual USB Port External Battery Bank for $21.95 shipped. Here is a screenshot for your reference. It charges 2 devices simultaneously and is compatible with most smartphones, tablets and other devices. You can check out the reviews on Amazon, which at the time of this post, has received an average of 4.7 out of 5 stars after 250 user reviews.