Engadget Explains What a 20,000 mAh Power Bank Can Actually Charge
Engadget reports that a 20,000 mAh power bank stores about 74 Wh and delivers roughly 60 to 70 percent usable capacity, enough for three to four iPhone 17 charges but only about one laptop charge.
Battery capacity is usually expressed in milliamp-hours, but Engadget said that number can overstate real-world performance. Internal resistance, heat and energy loss during charging and discharging reduce usable capacity to around 60 to 70 percent. A more reliable comparison is watt-hours, calculated from milliamp-hours multiplied by voltage and divided by 1,000. A 20,000 mAh lithium-ion power bank at 3.7V stores about 74 Wh, while 10,000 mAh and 5,000 mAh models store less.
The publication used several devices to show what that energy can power. An Apple iPhone 17 with a 3,692 mAh battery at 3.88V stores 14.3 Wh, so Engadget estimated it could receive three to four full charges from a 20,000 mAh power bank. An iPhone 17 Pro Max, with a 4,823 mAh battery at 3.88V and 18.7 Wh, could get two to three charges. A Steam Deck, with a 5,313 mAh battery at 7.7V and 40.9 Wh, could get one to one and a half charges. A laptop such as the M5 MacBook Air 13-inch, whose battery is rated at 53.8 Wh, would drain the power bank with a single charge.
Engadget said the capacity is not overkill for users who rely on a phone as a wireless hotspot or navigational tool, or who go camping or visit sites without outlets for full days or multiple days. It is also useful for avoiding constant checks of battery percentages. For people who do not need multiple charges, smaller 5,000 mAh power banks from companies such as Anker are lighter, occupy less space, and some can attach magnetically to a phone.
A 20,000 mAh power bank also falls under the 100 Wh airline limit, so Engadget said it can be carried in carry-on luggage on flights. The article advised that travelers who only need to charge a smartphone can use the larger power bank for multiple days, while commuters with lighter needs should consider a smaller model. It added that buyers should check charging speeds because the best power banks support fast charging.
Editor's Summary Engadget's Sept. 28 explainer says a 20,000 mAh power bank stores about 74 Wh and provides roughly 60 to 70 percent usable capacity, enough for multiple phone charges but generally one laptop charge. It advises buyers to compare watt-hours and device battery capacity, and to choose smaller models for daily commuting while checking fast-charging support.