How many mAh do I actually need?

Divide the power bank mAh by your phone's battery capacity, then multiply by 0.7 (energy loss during transfer). Example: 10,000mAh ÷ 4,000mAh phone × 0.7 = 1.75 full charges. For daily carry, 5,000 10,000mAh (1 2 charges) is sufficient. For travel days, 20,000mAh+. For camping/extended trips, 30,000mAh. More mAh = more weight, so carry only what you need.