Which power bank do I need? mAh, watts and sizes explained
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Your power bank should get you through the day reliably – but the choice is huge: 5,000, 10,000 or a full 20,000 mAh? Are 20 watts enough, or do you need 100? And why doesn't that "10,000" bank charge your phone three times, like you had calculated? In this guide you'll learn what the mAh figure really means, which size class fits your everyday life, and what to watch out for when charging a laptop, using MagSafe and flying.
mAh explained honestly: why 10,000 isn't really 10,000
The capacity on the packaging refers to the battery cells inside – measured at their nominal voltage of 3.7 volts. Your smartphone, however, charges over USB at 5 volts or more. The power bank's electronics have to step up the voltage, and part of the energy is lost as heat in the process. On top of that come losses in the cable and in your phone's charging circuitry.
The rule of thumb: divide the printed capacity by 1.4 to 1.5 to get the energy you can actually use. A sample calculation:
- Stated: 10,000 mAh (at 3.7 V)
- Actually usable: 10,000 ÷ 1.45 ≈ 6,900 mAh
- iPhone battery: around 3,500–3,700 mAh on current models
- Result: just under 2 full charges – not 3, as the raw mAh maths would suggest
That's why reputable brands like Anker or Baseus also state the energy in watt-hours (Wh). That figure is more honest – and it also decides whether your power bank is allowed on a plane (more on that below).
The three size classes at a glance
| Class | Weight (approx.) | Ideal for |
|---|---|---|
| 5,000 mAh | 100–150 g | Emergency reserve for your jacket or handbag, about 1 phone charge |
| 10,000 mAh | 180–250 g | Everyday use and commuting, 1.5–2 phone charges |
| 20,000 mAh and up | 350–500 g | Travel, tablet and laptop, 3–4 phone charges |
For most people the 10,000 model is the sweet spot: enough reserve for a long day, yet still compact. Go for a 20,000 model if you power several devices or spend longer stretches away from a socket.
Charging a laptop: it's all about the watts
If you want to charge a notebook, it's not just capacity that counts but above all the output power. Your laptop charges via USB-C Power Delivery (PD) – and depending on the model it needs between 45 and 100 watts: compact ultrabooks from around 45–70 W, powerful 14- to 16-inch machines more like 90–100 W. If the power bank delivers less, the laptop charges slowly, only while asleep – or not at all.
Pay attention to three things. First, the power bank's USB-C port must deliver the required PD output (e.g. "PD 65W" or "PD 100W"). Second, the cable has to keep up – for more than 60 W you need a USB-C cable with an e-marker chip (rated for 100 W or 240 W). Third, PPS (Programmable Power Supply) is worth having: this PD extension adjusts the voltage continuously and charges Samsung Galaxy models with "Super Fast Charging" noticeably faster.
Magnetic charging: MagSafe and Qi2
Magnetic power banks snap straight onto the back of your phone – no cable, no fiddling. They work with every iPhone from the iPhone 12 onwards (MagSafe) and increasingly with Android devices that support the Qi2 standard with a magnetic ring. Qi2 charges wirelessly at up to 15 W, the newer Qi2 25W standard (also called "Qi2.2") at up to 25 W.
Keep in mind: wireless charging is less efficient than charging by cable – so you get slightly fewer charges out of the same capacity. For on the go, magnetic models with 5,000 to 10,000 mAh are the best compromise between grip, weight and reserve.
What else to look for
- Ports: Two ports (USB-C plus USB-A, or two USB-C) charge your phone and earbuds at the same time. Models with a built-in cable are handy – one less thing to forget.
- Passthrough charging: The power bank hangs on the wall charger and charges your phone at the same time – ideal on the nightstand or in a hotel room with only one free socket.
- Display: A small display with a percentage readout is far more accurate than four LED dots.
- Weight: Be honest about what you'll carry every day – the best power bank is useless if it stays at home.
- Flying: Power banks belong exclusively in your carry-on and may not exceed 100 Wh – that's roughly 27,000 mAh. Many airlines, including SWISS and Edelweiss since January 2026, also allow a maximum of two per person and prohibit stowing them in the overhead bin. Check your airline's rules before departure.
Decision guide: which power bank for whom?
| User type | Recommended capacity | Recommended output |
|---|---|---|
| Emergency reserve on the go | 5,000 mAh | 20–22.5 W |
| Commuting and everyday use | 10,000 mAh | 20–30 W |
| iPhone or Qi2 users (wireless) | 5,000–10,000 mAh, magnetic | 15–25 W wireless |
| Frequent travellers with phone and tablet | 20,000 mAh | 30–65 W |
| Laptop users on the road | 20,000–25,000 mAh | 65–100 W PD |
| Multi-day trips and camping | 25,000 mAh (under 100 Wh) | 30–65 W |
Verdict
For most people a 10,000 model with 20–30 W is plenty – just divide the mAh figure by 1.4 to 1.5 and you won't be caught out. Laptop users should look at the PD wattage first, while iPhone and Qi2 fans benefit from magnetic models. In our range of power banks you'll find tested models from Anker, Baseus and co. – with a 30-day cooling-off period and a 2-year warranty.