As I’ve learned from using Anker’s PowerCore Fusion, USB battery packs are way easier to keep charged when they can plug straight into the wall. This 9,000mAh model from RAVPower has folding prongs, and even a built-in Lightning cable for Apple devices, in addition to a USB port that can accept any cable.

It might not be the best fit for you, but if you have any less tech-savvy iPhone owners on your holiday shopping list—the kinds of people who are unlikely to remember to pack an extra wall charger and microUSB cable to keep a battery charged—this would be a great gift.