Anker’s PowerCore battery packs are by far our readers’ favorites, and the 15,600mAh model is within a buck of the best price we’ve seen today with promo code ANK15600. While it’s probably too big to keep in your pocket, it’s worth keeping a battery of this size handy for long flights, camping trips, power outages, and any other situation where you’ll be without reliable charging for an extended period. It’s even big enough to share, if you’re feeling generous.