How big a power bank do you need?

How this works

Energy your devices need. For each device we multiply its battery size in watt-hours by the full charges it uses per day and the days you are away, then take off one charge if it starts the trip full. Phone sizes are the makers' typical capacities: 4,000 mAh for the Galaxy S25, 4,970 mAh for the Pixel 10, and 5,200 mAh for the Pixel 10 Pro XL. To turn mAh into watt-hours we assume 3.85V, a typical modern lithium-ion cell voltage; if your device lists watt-hours, enter that instead.

How much of the bank reaches your batteries. We assume 65% by default. That is our planning figure, not a published standard, and it sits below the numbers measured at the bank's own port: Anker puts typical conversion at about 82%, and The Verge measured 86.1% for the Nitecore NB10000 Gen4. The phone then loses more charging its own battery. As a check, The Verge's 39Wh Gen4 refilled an iPhone 15 Pro twice with a few watt-hours left. Pick 60% for older banks or wireless charging, 70% if you want the optimistic case.

Cold. Batteries give back less energy in the cold. CleverHiker measured a 13% efficiency drop for the NB10000 Gen4 in its cold test, one of the bigger drops it recorded, so the cold setting multiplies efficiency by 0.87. Keep the bank in an inside pocket by day and in your sleeping bag at night.

Default charge rates. Treeline Review's battery guide expects 4 to 5 phone charges over a week on trail, a headlamp charge every 3 to 5 nights, a GPS watch charge every other day, and a satellite messenger that rarely needs a recharge inside a week. Those set the defaults; change any of them to match how you use your gear.

Flying. FAA rules allow spare lithium batteries up to 100Wh in carry-on bags, 100 to 160Wh with airline approval, and nothing larger; power banks never go in checked bags. The 2026 international baseline adds a two-bank limit, and airlines can be stricter. Our airline power bank rules checker has carrier-by-carrier limits.

Picks. The calculator recommends only banks and stations from our guides with a published watt-hour rating, using one unit or a small multiple (two banks, say) that covers your need. Backpacking picks sort by carried weight, flying picks by fewest banks, and car camping picks by the smallest unit that covers it. The INIU Pocket Rocket P50 and P41 are not included because INIU does not publish a watt-hour rating, and the two home-backup stations in our power station guide are left out because they are not trip gear.