Will your phone and internet work in a power cut?
Probably not, unless something keeps the router powered. UK landlines are moving from the old copper network to digital phone lines, which the industry aims to finish by 31 January 2027. A digital landline phone plugs into the broadband router, so when the router goes off, the home phone goes with it. So does Wi-Fi calling.
Mobile phones keep working as long as their batteries and the local masts do, but masts have limited backup power of their own, so a long cut can take mobile signal down too.
If you rely on the landline, ask your provider
Ofcom requires phone providers to offer customers who depend on their landline, for example because they have no mobile signal at home or rely on a telecare alarm, a free way to call 999 for at least an hour in a power cut. It is usually a small battery unit for the router. Ask your provider if that applies to you or someone you look after, and tell them about any telecare or alarm equipment on the line.
Keeping the router on yourself
A router draws roughly 6 to 12 W, and a fibre connection adds a second box on the wall (the ONT) that needs power too. That is a small load, so modest batteries last a useful time:
| Option | Router, about | Worth knowing |
|---|---|---|
| Mini UPS made for routers | Several hours | Sits between the adapter and the router, switches over by itself. Match its DC outputs to your router's voltage. |
| 10,000 mAh power bank | 2 h 30 min | Needs a USB-to-12 V cable and a bank that supports it; you plug it in by hand. |
| 20,000 mAh power bank | 5 h | Same cable caveat. Doubles as the phone charger. |
| Anker SOLIX C300 | 11 h 38 min | Through the mains socket; the 12 V or USB-C output lasts longer still. |
| Anker SOLIX C1000 | 36 h 33 min | And the fridge, the lights and the phones at the same time. |
The cheap options
Mini UPS for the router. Home phones now run through the broadband router, so when it goes off in a power cut the landline goes with it. A small battery box keeps the router, and the phone plugged into it, working.
Look for: DC outputs that match the voltage printed on your router's power adapter (usually 12 V), enough of them for the fibre box too if you have one, and a capacity in watt-hours.
Power bank, 20,000 mAh. Keeps a phone going for days if you use it sparingly.
Look for: Capacity in watt-hours as well as mAh (about 74 Wh for 20,000 mAh), USB-C in and out, and keep it charged.
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Before you buy a router UPS
- Read the router's power adapter. It says the voltage (usually 12 V) and current it needs. The UPS output must match, and the plug must fit.
- Count the boxes. With full fibre you need to power the router and the ONT. Some units have two outputs for exactly this.
- Check the watt-hours, not only the mAh. Divide by the watts your boxes draw for a rough upper limit on the hours.
- Telecare and alarms should be checked with their provider: some need their own backup, and a test on a calm day is worth doing.
In the US, phone service through a cable or fiber modem stops in an outage the same way unless the modem has battery backup; ask your provider what it offers. The power cut essentials list and its US edition cover the rest of the kit.
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