Almost everyone buys a power bank looking only at the mAh — and almost everyone gets a surprise when their “10,000 mAh” doesn’t charge the phone twice fully. This guide explains why that happens and what to actually look at, so you buy a power bank that delivers what you expect. Spoiler: the big number on the box is the one you should look at least.
The 4 criteria that truly decide (and why)
1. Real capacity, not the advertised one. A power bank loses energy converting its internal voltage to the phone’s: you only use 60–70% of the label’s mAh. So a “10,000 mAh” delivers about 6,500–7,000 real mAh — barely a charge and a half for a modern phone. Why it matters: it avoids disappointment. If you want two full charges, aim for 20,000 nominal mAh.
2. Power (watts and USB-C PD). Watts (W) decide the speed. An 18 W port charges a phone slowly; 30–65 W does it fast; to charge a laptop you need USB-C Power Delivery (PD) of 65–100 W. Why it matters: a huge battery is useless if it takes three hours to move the energy to your device.
3. Qi2 magnetic charging (if you have a compatible phone). Qi2 (and the new Qi2.2, up to 25 W) lets the battery snap onto the phone and charge without a cable, with magnets that keep it aligned. Why it matters: it’s the ultimate convenience for iPhone 17, Pixel 10 and phones with Qi2 accessories — stick it on and keep using the phone. Note: without Qi2 certification, many “magnetic” ones drop to 7.5 W and slip off.
4. GaN technology, ports and weight. Power banks and chargers with gallium nitride (GaN) are 20–30% smaller and more efficient at the same capacity. Also check how many ports it has (to charge several devices) and the weight. Why it matters: for air travel there’s a legal limit of 100 Wh (≈ 27,000 mAh); above that, you can’t take it on board.
How to choose by use case
| Your case | Look for | Typical capacity |
|---|---|---|
| Everyday in your pocket | Lightweight + Qi2 | 5,000–10,000 mAh |
| Travel / weekend | 2 charges + fast PD | 20,000 mAh |
| Charge the laptop too | USB-C PD 65–100 W (GaN) | 20,000 mAh+ |
| iPhone/Pixel cable-free | Qi2 / Qi2.2 magnetic | 5,000–10,000 mAh |
Our recommendations (applying the above)
For everyday, cable-free → a Qi2 magnetic 10,000 mAh power bank. It snaps onto the phone and charges while you use it; look for one Qi2 certified (brands like Anker MagGo or Belkin) so it doesn’t drop to 7.5 W.
🛒 Check Qi2 magnetic power banksFor travel → a 20,000 mAh battery with USB-C PD. Two real phone charges and power for a tablet; below the airline limit.
🛒 Check 20,000 mAh power banksTo charge the laptop too → a 65–100 W GaN charger/station. A single device for phone, tablet and laptop; gallium ones are small and don’t get hot.
🛒 Check 100 W GaN chargersFrequently asked questions
Why doesn’t my 10,000 mAh power bank charge my phone twice? Because you only use 60–70% of those mAh due to conversion losses, and your phone already has 4,000–5,000 mAh. For two full charges you need 20,000 nominal mAh.
How many watts do I need? For the phone, 30 W is already comfortable fast charging; if you want to charge a laptop, aim for 65–100 W with USB-C Power Delivery.
Can I take the power bank on a plane? Yes, in your carry-on and below 100 Wh (≈ 27,000 mAh). Higher-capacity ones require authorization or aren’t allowed.
Looking for more accessories? See the best gadgets for your phone or how to choose the best smartwatch.
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