content: Best external phone battery? I have a Droid Turbo 2 (3760 mAh battery) and will be taking some trans-Pacific flights later this year.  I expect to use my phone extensively for audiobooks, and outlets are hard to find in airports, so keeping it powered is a priority.  My phone's battery isn't removable, so I can't just swap it out. Does anyone have recommendations for external USB-connected phone batteries?  Maximizing battery life is a priority.