Best power banks for power cuts: a UK buying guide

How much power you really need to keep phones running for a week without electricity, and how to spot unrealistic claims.

A solar power bank charging a phone next to an LED lantern and head torch

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Quick answerThe best power bank for a power cut is a 10,000–20,000mAh bank from a reputable maker with UKCA or CE marking and a clearly printed watt-hour (Wh) rating, kept fully charged. 10,000mAh gives about two phone charges. Treat built-in solar panels as a slow top-up only, and be wary of pocket-sized banks claiming 50,000mAh.

How much capacity do you need?

Capacity	Approx. Wh	Typical phone charges	Good for
5,000mAh	18.5Wh	About 1	Handbag backup
10,000mAh	37Wh	About 2	1–3 days with careful use
20,000mAh	74Wh	About 4	A week for one phone
26,800mAh	99Wh	About 5–6	Largest common size under 100Wh

Wh = mAh × 3.7V ÷ 1000. Real-world charges are lower than the headline because of conversion losses.

Buying checklist

UKCA or CE mark and a UK importer or manufacturer address on the box
Watt-hour rating printed on the case
USB-C input and output (faster to recharge)
Pass-through or LED charge indicator
Realistic size and weight for the capacity claimed

Make your phone battery last

Low-power mode on. Cuts background activity.
Dim the screen. The screen is the biggest drain.
Text, don't call. Texts get through more reliably and use less power.
Charge in short bursts. Top up from 20% to 80% rather than 0 to 100.

Frequently asked questions

What size power bank do I need for a power cut?

For a day or two, 10,000mAh gives most phones two full charges. For a week, aim for 20,000mAh or two 10,000mAh banks, plus a solar or hand-crank backup. Larger is heavier and slower to recharge.

Are solar power banks any good?

The small panel on a solar power bank charges very slowly, often taking days in UK daylight. Treat solar as a trickle top-up and charge the bank fully from the mains before you need it.

Can a power bank really be 50,000mAh?

Some cheap listings claim 50,000mAh or more in a pocket-sized case, which is usually unrealistic. A genuine 50,000mAh bank is large and heavy and is around 185Wh, above the 100Wh limit airlines and many couriers use. Check the watt-hour (Wh) rating on the label.

How do I keep a power bank ready for emergencies?

Charge it to full, store it somewhere cool, and top it up every 1–3 months. Lithium batteries slowly self-discharge.

Updated 2026-10-28.