How Long Will It Run

How to keep warm in a power cut

Warm the people, not the house. Without power most central heating stops, and no battery you can carry will heat a room for long. What works is keeping body heat in: one room, layers, hot water bottles and a bed full of blankets.

Before it gets cold

Warmth that needs no socket

Hot water bottle and a vacuum flask. Boil water while you still can, keep it hot in a flask, and refill the bottle through the night.

Look for: A bottle made to BS 1970 in the UK, and a flask of a litre or more.

Fleece blankets or sleeping bags. Layers and a warm bed do more than any heater a battery can run.

Look for: Whatever you would take camping; a sleeping bag rated for the season is warmer than a duvet.

Hand warmers. Air-activated packs give hours of heat with no power at all, and a pocketful helps children and older relatives.

Look for: Long-duration packs, and the expiry date on bulk boxes.

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What a battery can heat

An electric heater is the worst job you can give a battery. A 2,000 W fan heater is more than a 1,056 Wh Anker SOLIX C1000 can even start, and even a small 750 W heater lasts about 1 h 1 min. The heater guide has the full sums.

Heat next to the body is different. The same station runs a mains electric blanket for about 23 h 59 min. Without a station, a 20,000 mAh power bank runs a USB heated throw for about 7 h 24 min or a USB heated gilet for about 7 h 24 min on a medium setting.

If your heating is a gas combi boiler or a furnace, its electrics need far less than a heater: see the boiler guide or the furnace guide.

Battery carbon monoxide alarm. Anything burning fuel indoors, a boiler relit after an outage included, can produce carbon monoxide you cannot see or smell.

Look for: A sealed long-life battery and EN 50291 certification in the UK (UL 2034 in the US).

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Look after the people most at risk

Babies, older people and anyone who is unwell lose heat faster and notice it later. Check on neighbours who live alone. In Great Britain, anyone who relies on medical equipment, is of pensionable age or has a young child can join their network operator's Priority Services Register for extra help in a power cut; call 105 to report a cut or ask about it.

The power cut essentials list covers light, phones and food as well, and the US edition adds frozen pipes.