Power banks are one of those categories where marketing numbers and reality routinely part ways. We tested five popular 20,000mAh models with identical loads, measuring real delivered capacity, charging speed, and heat.

The results surprised us

Delivered capacity ranged from 62% to 88% of the advertised figure — a gap big enough to mean an entire extra phone charge. Fast-charging claims held up better, though two units throttled noticeably once they warmed up.

What to look for when buying

Prioritize banks that list delivered (rated) capacity honestly, support the same fast-charging standard as your phone, and include pass-through charging if you travel. Weight matters more than you think — check it before you buy.

The full breakdown of our testing data, including charge curves for every unit, is coming in a follow-up piece for readers who want the numbers.