Power cut guide
How to Keep Your Wi-Fi On in a Power Cut
Quick answer: Your router, and your fibre box if you have full fibre, need mains power, so Wi-Fi goes off in a power cut unless you add a battery backup. A small “mini DC UPS” designed for routers is the cheapest and most efficient way to keep them going for several hours; a standard UPS or a portable power station also works. Even with backup, your internet can still drop if the local network equipment loses power too, so keep a charged mobile phone ready to use as a hotspot.
Is the power off where you are? See live power cuts from the network operators and reports from neighbours.
This guide is for anyone who works from home, relies on a digital landline, uses smart devices or simply wants to stay in touch during a power cut. It explains what equipment needs power, the different types of backup, how to estimate how long they will last, and what happens beyond your front door.
Why your Wi-Fi stops in a power cut
Your broadband connection depends on equipment in your home that plugs into the mains. Ofcom points out that routers and other home broadband equipment need mains power and usually have no battery of their own. When the power goes, so does your Wi-Fi, and so does any phone that runs through the router.
Which boxes you need to keep powered depends on your connection:
| Connection type | Equipment that needs power | Notes |
|---|---|---|
| Full fibre (FTTP) | Fibre box on the wall (often called an ONT) and router | Both must stay on. Fibre cannot carry electricity to your home. |
| Part fibre over phone line (FTTC, “superfast”) | Router | Relies on a powered street cabinet nearby. |
| Cable | Router or hub | Relies on the cable network’s own powered equipment. |
| 4G/5G home broadband | 4G/5G router | Relies on the local mobile mast having power. |
| Mesh Wi-Fi or extenders | Each extra unit | Usually only the main router needs backup; you can live without the extras. |
Will broadband still work if the whole street loses power?
Keeping your router on is only half the picture. Your connection also passes through equipment outside your home, such as street cabinets, local exchanges and, for 4G broadband, mobile masts. All of these need electricity too.
- Exchanges generally have backup power, which is why traditional copper phone lines used to keep working in a power cut.
- Street cabinets and other local equipment may have backup batteries, but there is no single guaranteed running time, and in a long or widespread power cut the connection can drop even if your router is still on.
- Mobile masts share the local electricity supply. Ofcom has said there is no explicit minimum power backup time set for mast sites; its updated 2026 resilience guidance expects mobile operators to manage power cut risks but does not set a fixed number of hours.
In practice, this means a battery backup is most useful for short and local power cuts, which are the most common kind. For a big storm that takes out power across a whole area, your broadband may go regardless, and the mobile network may become patchy as well.
To see how far a power cut has spread, check your postcode on our live map. You can also scan the list of power cuts today for nearby areas. A large cut covering several postcodes is a sign that local network equipment may struggle.
Option 1: a mini DC UPS for your router
A mini DC UPS is a small battery pack that sits between your router’s power adapter and the router itself. Most routers and fibre boxes actually run on low-voltage direct current (DC), typically 12V, from a plug-in adapter. A mini DC UPS supplies that DC directly from its battery, so there is no wasteful conversion to mains AC and back again.
- Pros: small, silent, low cost compared with other options, efficient, usually switches over with no break.
- Cons: limited capacity, and you must match the output voltages and plug sizes to your equipment.
Many models have two or more outputs, for example 12V and 9V, so you can power both a fibre box and a router from one unit.
Choosing one
- Read the label on each power adapter. Note the output voltage (for example 12V) and the current (for example 1.5A).
- Check the plug size and polarity. Many units come with adapter tips; make sure yours is included.
- Choose a UPS whose outputs match each voltage and can supply at least the current shown on the adapters.
- Look at the battery capacity, usually given in watt-hours (Wh) or milliamp-hours (mAh) at a stated voltage. Watt-hours are easier to compare.
Safety: Connecting the wrong voltage can damage your router or fibre box. If you are unsure, ask your broadband provider which power supply your equipment uses. Do not open the fibre box on the wall.
Option 2: a standard UPS
A standard uninterruptible power supply (UPS) is the kind used for desktop computers. It plugs into the wall and gives you a few mains sockets that keep working on battery when the power fails. You plug your router’s normal adapter into it.
- Pros: simple, no voltage matching, can also protect a desktop computer long enough to save your work and shut down.
- Cons: bulkier, often has a fan or beeps, and wastes some energy converting battery power back to AC, so runtime is shorter than its battery size suggests.
Standard UPS units are usually designed to keep a computer going for minutes, not hours. For a router alone they last longer, but a mini DC UPS of a similar size will usually do better. If you work from home, our guide to power cuts and working from home covers protecting computers and data as well.
Option 3: a portable power station
If you already have a portable power station, or want one for lights, phones and other devices, it can run your router for many hours. Some can act as a basic UPS, switching over automatically when the mains fails. Check how quickly the switch happens, as a brief gap may make the router restart.
Our guide on choosing a portable power station for power cuts explains how to compare capacity and output.
Quick comparison
| Mini DC UPS | Standard UPS | Portable power station | |
|---|---|---|---|
| Size | Small, like a power bank | Medium box | Large and heavy |
| Efficiency for a router | High | Lower (AC conversion) | Better if using its 12V or USB-C output |
| Typical use | Router and fibre box only | Router plus PC shutdown | Router plus lights, phones, laptop |
| Noise | Silent | May beep or have a fan | Usually quiet, fan under load |
| Set-up | Match voltages and plugs | Plug and go | Plug and go |
How long will it last? A runtime estimate
You can estimate runtime with simple sums. The figures below are examples, so use the numbers from your own equipment.
Say your router’s adapter is labelled 12V 1.5A and your fibre box’s adapter is 12V 1A.
- Maximum power: router 12 x 1.5 = 18W; fibre box 12 x 1 = 12W. Total 30W.
- Labels show the most an adapter can supply, and equipment often uses noticeably less. If you can measure it with a plug-in energy meter, use that figure. Otherwise 30W is a safe upper estimate.
- Take the backup’s capacity in watt-hours and allow for losses. For a mini DC UPS, assuming about 85% usable is a cautious planning figure; for an AC UPS or power station AC socket, assume less, around 80%.
- Runtime = usable Wh ÷ watts. A 60Wh mini DC UPS: 60 x 0.85 ÷ 30 = about 1.7 hours at the worst case. If the real draw is 15W, that becomes about 3.4 hours.
Our battery backup calculator can do this for you. If you rely on your connection for a digital landline, aim for more than the minimum, as many power cuts last longer than an hour or two.
Tip: Turn off Wi-Fi extenders, smart speakers and anything else on the battery that you do not need. Every watt you save adds time.
Your mobile phone as a backup hotspot
If your broadband drops, your phone’s mobile data can share an internet connection with a laptop or tablet. This works as long as the local mast has power and signal.
- Learn how to turn on your phone’s personal hotspot now, before you need it.
- Check your mobile data allowance. Video calls and downloads use a lot.
- Hotspot use drains your phone battery quickly, so keep it plugged into a power bank.
- Keep the hotspot for essentials, and save some battery for calls.
Ofcom advises keeping a charged mobile phone as a backup for power cuts anyway. GOV.UK also notes that you can make 999 calls on any mobile network, even if your own provider has no signal.
If you have a digital landline
If your home phone now plugs into your router, it will stop working when the router does. Ofcom requires providers to make sure customers can contact the emergency services in a power cut, and its guidance says providers should offer at least one solution giving at least an hour of access, free to customers who are at risk because they depend on their landline. A battery backup unit supplied by your provider counts.
Our guide will my phone, broadband and landline work in a power cut? explains your rights and what to ask your provider. A Wi-Fi backup is one item in a wider plan, which our power cut emergency kit guide sets out.
Frequently asked questions
Does broadband work in a power cut?
Not without backup. Your router needs mains power. With a battery backup it can keep working, as long as the local network equipment outside your home still has power too.
How long will a UPS keep my router on?
It depends on the UPS capacity and your equipment’s power use. Divide the usable watt-hours by the watts your router and fibre box use. Small mini DC UPS units often give a few hours for a typical router.
Is a mini DC UPS better than a normal UPS for a router?
For a router alone, usually yes. It is smaller, quieter and more efficient because it supplies DC directly instead of converting to AC. A standard UPS is better if you also need to keep a desktop computer running briefly.
Will my full fibre battery backup unit keep the internet on?
Not necessarily. Older full fibre installs sometimes included a battery for the fibre box, but the router also needs power for the internet or phone to work. Ask your provider what backup they supply.
Can I use my car to charge devices in a power cut?
You can charge a phone from a car’s USB or 12V socket. Never run the engine in a garage or enclosed space, because exhaust fumes contain carbon monoxide.
Your next step: look at the labels on your router and fibre box today and note the voltage and current. That tells you which backup will fit, and how long it is likely to last.
Sources
- Ofcom u2013 Landlines and power cuts
- GOV.UK u2013 UK transition from analogue to digital landlines
- Ofcom u2013 FOI response: power backups and the switch to digital voice
- ISPreview u2013 Ofcom update guidance on power backup and resilience in UK mobile networks (June 2026)
- ISPreview u2013 Openreach to stop providing battery backup for FTTP broadband
Checked against these sources on 28 October 2026. Rules and amounts can change – your network operator or Ofgem has the final word. Spotted something out of date? Tell us.
More on being prepared: Power Cut Emergency Kit: What to Keep at Home · All power cut guides