In a long power cut, your phone matters more, not less: it's your torch and your link to family, and it receives emergency alerts while the network lasts. Nineteen of the 24 national guides we compiled list a charged power bank, from Sweden and Finland to Portugal and Greece.
The short answer: 20,000 mAh per phone
A 20,000 mAh power bank gives most phones three to four full charges. Used carefully, a phone needs about one charge a day, so that's one phone for three days with a margin. Households with two adults should plan for two power banks, or one that's twice the size.
Why 20,000 mAh doesn't mean five charges
Phone batteries hold 4,000 to 5,000 mAh, so the sums seem to promise four or five charges. In practice you get less, for two reasons:
- Different voltages. The mAh figure on a power bank is measured at its cells' 3.6–3.7 V, then converted to the 5 V or more that USB uses. Watt-hours (Wh) are the honest figure: 20,000 mAh is about 74 Wh.
- Conversion losses. Heat and electronics lose around a third on the way. Of 74 Wh, roughly 45–50 Wh reach the phone.
A typical phone battery holds 15–19 Wh, which is how you get three or four charges.
| Capacity | Real phone charges | Good for |
|---|---|---|
| 10,000 mAh | 1.5–2 | A day out, a grab bag |
| 20,000 mAh | 3–4 | One phone for 72 hours |
| 27,000 mAh (99 Wh) | 5–6 | Two phones, or longer; the biggest allowed on planes |
| Power station (250+ Wh) | 15+ | Laptops, lights, a CPAP machine |
What to look for
- USB-C in and out. One cable for everything, and fast recharging when the power briefly comes back.
- Two or more ports, to charge a phone and a radio or torch at once.
- A charge indicator that shows percentage or at least four steps, so you know what's left.
- A known brand. Cheap no-name power banks often overstate capacity and skip safety circuits.
- Skip built-in solar panels. The small panels on power banks take days of full sun to make a dent, and a northern winter week gives almost nothing.
Keep it charged
A power bank is only useful if it's full when the power goes. Lithium cells lose a little charge every month, so top it up every three months. Doing it at the same time as checking the rest of your kit makes it easy to remember. Store a cable with it, rubber-banded on, and keep it somewhere cool: heat ages the battery and cold cuts its capacity for a while.
Make every charge last
- Switch the phone to low-power mode at the start of the outage, not when it reaches 20%.
- Turn off Wi-Fi and Bluetooth, and turn the screen brightness down.
- Send texts rather than calling: messages get through on congested networks when calls don't.
- Use a battery radio for news instead of streaming.
- A car with fuel is a charger too. A USB car charger turns the car into a charging station, but run the engine outdoors only.
Do you need a power station?
For most households, no: a power bank, a battery radio and torches cover 72 hours. A portable power station (a large battery with mains sockets) makes sense if someone depends on powered medical equipment, or if you want to run a laptop or lights for a week. Ask your doctor or equipment supplier first about backup power for medical devices.
The rest of your power kit
Your phone isn't the only thing that needs power. Spare batteries for the radio and torches are on 22 of 24 lists. Lithium AA cells keep for years and work in the cold.
See the full 72-hour emergency kit checklist, or work out your household's kit.