In a power cut, your phone is your torch backup, your news source, your way to call 105 and your link to family. A charged power bank keeps it alive. But the numbers on the box are confusing, and plenty of power banks are poor value. Here’s what to look for.
The short version
- For most people, a 10,000mAh power bank is the sweet spot.
- For a family, or a longer cut, go for 20,000mAh.
- Expect about 60–70% of the box capacity to reach your phone.
- Keep it charged, and top it up every three months.
- Skip tiny solar power banks and wind-up phone chargers.
What the numbers mean
Power bank capacity is usually given in mAh (milliamp hours). Bigger is more charge, but you don’t get it all:
- Some energy is lost converting the battery’s voltage to charge your phone.
- In practice, expect around 60–70% of the stated capacity to reach your phone.
- Most modern phones have batteries of roughly 4,000–5,000mAh.
As a rough guide:
- 10,000mAh: about 1.5 to 2 full phone charges.
- 20,000mAh: about 3 to 4 full phone charges.
Some power banks also give capacity in Wh (watt hours), which is a more honest figure. A 10,000mAh power bank is usually about 37Wh.
Our picks
We haven’t added specific product links yet. These are the features to look for.
Budget pick: a 10,000mAh pocket power bank. Plenty for one person over a weekend-long power cut. Look for USB-C in and out, and a charge level indicator so you can tell at a glance how full it is.
Worth paying more: a 20,000mAh power bank with USB-C PD. “PD” (Power Delivery) means faster charging, and it can top up several phones, a tablet, or a USB head torch. Ideal for a family. It’s heavier, but it lives in your kit box, not your pocket.
For bigger outages: a portable power station. These can run a low-wattage electric blanket, a router or a laptop, but they cost far more. We’ll cover whether they’re worth it in a future Kit Check.
What to skip
- Small “solar power banks”. The tiny panel takes days to charge anything, especially in a UK winter.
- Wind-up phone chargers. Minutes of cranking gives seconds of charge.
- No-name power banks with huge claims. “50,000mAh” for £10 is not real. Buy from known brands and reputable retailers, and check for UK safety markings.
Look after it
- Charge it fully before winter, and top it up every three months. Power banks slowly lose charge when stored.
- Store it indoors at room temperature, not in a cold car or loft.
- Don’t leave it charging overnight on a bed or sofa.
- If it ever swells, gets hot or smells odd, stop using it and recycle it properly.
Make your phone last longer
- Turn screen brightness right down and switch on battery-saving mode.
- Close apps you don’t need and turn off Bluetooth.
- Text rather than call.
- Use a separate torch rather than your phone’s light.
3 things to do this week
- Find any power banks you already own and charge them fully.
- Check they have the right cable for each phone in your house.
- Set a reminder to recharge them every three months.
This fits into our 72-hour blackout kit for under £50. Some links on this site may be affiliate links. See our affiliate disclosure.