How to keep Wi‑Fi running in a power cut (UK)

Power cuts are annoying. Losing Wi‑Fi during a power cut is deeply personal.

The good news: keeping your internet up is usually one of the easiest backup-power wins, because your router doesn’t need much power.

This guide covers the simple setups that work in UK homes, what to plug in, and how to estimate how long it’ll last.

The first thing to understand: you might need to power two boxes

Depending on your setup, “the internet” might be:

• Router (Wi‑Fi box)
• Modem / ONT (the fibre/phone-line box)

If you’ve got full fibre (FTTP) you usually have an ONT (often a small Openreach box). If you don’t power the ONT, your router can be alive and cheerful… with nothing to talk to.

Quick test: look near where the fibre/phone line comes in. If there’s a second small box with lights, assume it needs power too.

Option A (recommended): a small portable power station

A portable power station (battery + inverter) is the easiest because it can run:

• router + ONT
• phone chargers
• a laptop
• a lamp

…and generally doesn’t involve you becoming an electrical engineer.

What size do you need for Wi‑Fi?

Typical power use: - Router: 8–15W - ONT/modem: 5–10W

Call it 20W total to be safe.

Rough runtime estimate: - Runtime (hours) ≈ (battery Wh × 0.8) ÷ load W

Example: - 256Wh power station → usable ~205Wh - 205Wh ÷ 20W ≈ 10 hours

So even a small unit can keep your internet up most of the day.

What to buy (quick rule)

• 300Wh-ish is plenty for router+ONT overnight
• 500Wh+ gives you headroom for charging phones/laptops without stressing

(We list recommended models here: best portable power stations (UK).)

Option B: a UPS (Uninterruptible Power Supply)

A UPS is the thing offices use so computers don’t instantly die.

Pros: - Instant switchover (no reboot) - Usually great for router+ONT

Cons: - Often noisy (fan) or beepy - Runtime is usually shorter for the money - Some models output a “stepped” waveform that fussy adapters don’t love

If you want “zero faff” and you only care about internet, a UPS can be ideal.

Option C: USB‑C / DC backup (only for nerds)

Some routers can run from DC barrel jacks or USB‑C, and you can use a big USB power bank.

It can work. It can also turn into an afternoon of adapters and regret.

If you’re not sure, skip this and use a power station.

Practical tips (things that trip people up)

1) Your Wi‑Fi name might still appear even if the internet is down

Your router can broadcast Wi‑Fi even if the ONT/modem is dead.

So if the kids shout “Wi‑Fi’s back!”, that may just mean the router has power.

2) During a big outage, your ISP equipment may go down too

If there’s a wider network outage, powering your gear won’t magically revive the street cabinet.

Still worth doing, because short local outages are common.

3) Put the router + ONT on one extension lead

Plug both into the backup power via one extension lead so you don’t forget one.

4) Keep a cheap LED lamp nearby

Wi‑Fi in a dark house is a bit bleak. A small LED lamp makes the whole setup feel… less apocalyptic.

Quick checklist

• [ ] Identify whether you have router only, or router + ONT/modem
• [ ] Add up watts (or assume ~20W)
• [ ] Choose backup: power station or UPS
• [ ] Test it once (seriously — don’t discover a problem mid-storm)

Next reads

• Best portable power stations for UK power cuts (2026): /best-portable-power-stations-uk/
• Can a power station run a fridge? (UK): /can-a-power-station-run-a-fridge/