10,000 or 20,000 mAh? The Power Bank Math Nobody Tells You

Quick answer: 10,000 mAh ≈ 1.5–2 full iPhone charges and fits in a pocket. 20,000 mAh ≈ 3–4 charges for trips and long days. Choose USB-C PD (20W+), and MagSafe if you want cable-free top-ups.

Power bank boxes love big numbers. But a 10,000 mAh bank won’t charge your iPhone three times, no matter what the seller says. Here’s why — and what to buy.

The real math

Power banks are rated at the battery cell’s voltage (about 3.7V). Converting that to the 5–9V your phone needs, plus heat and cable losses, eats roughly 30–40% of the capacity. So a 10,000 mAh bank delivers around 6,000–7,000 mAh to your phone — about 1.5 to 2 full charges for most iPhones.

Which size fits you?

Features worth paying for

• USB-C PD 20W or more — fast charging on the go.
• Two outputs — charge phone and AirPods together.
• Pass-through charging — charge the bank and phone at once.
• A real brand — Anker, Baseus, UGREEN. Cheap banks lie about capacity.

Flying?

Power banks must go in your carry-on, never checked luggage. Under 100 Wh (about 27,000 mAh at 3.7V) is generally allowed; always check your airline. More in our flying guide.

Shop all power banks or see whether MagSafe power banks are worth it.