The most dependable way to keep internet access during a power cut is to prepare two separate routes. Use a suitable battery supply to keep your broadband router and any separate modem or fibre terminal powered, and retain mobile data as a fallback through a charged phone or dedicated hotspot. Either route can still fail if the provider’s network equipment or local mobile mast loses service, so no household setup can guarantee an uninterrupted connection.
For a short local outage, a small router backup or uninterruptible power supply may be enough. A power bank can keep phones and some USB-powered hotspots running, while a portable power station can support a router, fibre terminal and several chargers for longer. Test the complete arrangement before relying on it and keep an offline communications plan in case both fixed and mobile networks become unavailable.
Why home internet stops during a power cut
Your Wi-Fi signal is only the final part of the connection. The equipment inside the home needs electricity, and the wider provider network must also remain operational. Powering one device while overlooking another is a common reason a backup arrangement appears not to work.
| Connection type | Equipment that may need power at home | External dependency |
|---|---|---|
| Full-fibre broadband | Router and optical network terminal, usually called an ONT | Provider fibre network and its powered equipment |
| Part-fibre or copper broadband | Router, normally with its modem built in | Street cabinet, exchange and provider network |
| Cable broadband | Provider hub or separate modem and router | Provider’s local cable network and powered cabinets |
| 4G or 5G home broadband | Mobile router, phone or battery hotspot | Usable signal, capacity and power at the mobile mast |
| Satellite broadband | Satellite terminal, router and any separate power unit | Satellite service, provider ground systems and a clear view required by the equipment |
A powered router can continue providing a local Wi-Fi network even when its internet connection has disappeared. Devices may still show that they are connected to Wi-Fi, but websites and messages will not load. Check the router and network-terminal status lights, then use the provider’s service page or mobile app if another connection is available.
The UK Government’s power-cut guidance warns that home internet will not work without power and that mobile service may also stop if the local mast is affected. Most outages are short and local, but a longer or wider incident can exhaust backup power elsewhere in the communications network.
What to do when the power goes off
- Confirm that it is a power cut. Check whether neighbouring properties and street lighting are affected. Report or track the outage through Power Cut 105 in England, Scotland and Wales. In Northern Ireland, use Northern Ireland Electricity Networks.
- Protect your phone battery. Switch on low-power mode, reduce screen brightness and avoid using the phone as a torch. Keep at least one charged phone available for important calls.
- Test mobile data. Turn off Wi-Fi briefly and see whether the phone can load a lightweight webpage or send a message. Do not repeatedly refresh large sites if the network is congested.
- Connect backup power to the fixed-broadband equipment. Power the router and every essential upstream device in the home, including a fibre ONT or separate modem where fitted.
- Use one internet route at a time where practical. If mobile data works reliably, it may be more efficient to leave the fixed-broadband equipment off until it is needed. If fixed broadband works, avoid running a phone hotspot unnecessarily.
- Check official and provider updates. Save useful information, then reduce browsing to preserve battery capacity and network availability.
Turn off or unplug computers, televisions and other non-essential equipment that was operating when the cut began. The UK Government advises unplugging televisions and PCs because they may be damaged by a surge when electricity returns. Leave one light switched on if that will provide a clear indication that mains power has been restored.
Keep fixed broadband running with backup power
Identify every powered item between the incoming connection and your devices. A full-fibre service commonly has both an ONT and a router. Supplying the router alone will not keep the connection working if the ONT is off. A separate modem, mesh controller, network switch or cordless-phone base may also need power, depending on what services are essential.
Possible backup methods include:
- A communications-provider battery unit: designed for specific provider equipment, often with the main purpose of preserving digital phone access for a limited period.
- A small uninterruptible power supply: keeps compatible AC equipment running automatically when mains power fails. Check its watt rating, battery runtime at the actual load and whether its output is suitable for the connected equipment.
- A dedicated DC router backup: can avoid some inverter losses, but its output voltage, connector size, polarity and current capability must exactly match the equipment manufacturer’s requirements.
- A portable power station: can supply ordinary mains adaptors and charge several devices. Its own electronics consume energy, so the usable runtime may be lower than a simple capacity calculation suggests.
Our guide to the best portable power stations for home backup compares larger systems for routers and other selected essentials. If the priority is charging phones or running a USB hotspot, see the best power banks for power cuts.
Do not assume any power bank can run a router
A standard USB power bank is primarily intended to charge USB devices. Many routers use a round DC connector and require a fixed voltage that an ordinary USB outlet does not provide. A USB-C power bank, trigger cable or voltage-conversion lead should be used only when the power source, cable and router are explicitly compatible. The voltage and polarity must be correct, and the supply must be capable of providing at least the required current. A wrong or poor-quality adaptor can damage the router or create a fire risk.
Do not leave a general-purpose power bank permanently between the mains and a router unless the manufacturer states that it supports that use. Many power banks do not support simultaneous charging and discharging, and some interrupt their output when the input supply changes. A purpose-designed UPS is normally the clearer option when automatic, continuous switchover matters.
Calculate how long the router backup may last
Battery capacity is normally stated in watt-hours, while equipment demand is stated in watts. Add the actual demand of the router, ONT and any other equipment that must remain on, then use this planning formula:
Estimated runtime in hours = usable battery watt-hours ÷ total load in watts
Usable capacity is lower than the headline battery capacity because conversion, the inverter and the battery-management system consume energy. As a planning example, applying an 85% usable-capacity assumption to a 100 watt-hour battery gives 85 watt-hours. If a router and ONT draw 15 watts together, the estimate is 85 ÷ 15, or about 5.7 hours. This is an illustration, not a promised runtime.
| Example battery | Illustrative usable energy at 85% | Runtime at a 15 watt load |
|---|---|---|
| 100 watt-hours | 85 watt-hours | About 5.7 hours |
| 256 watt-hours | 218 watt-hours | About 14.5 hours |
| 512 watt-hours | 435 watt-hours | About 29 hours |
Actual runtime can be shorter because of inverter standby consumption, battery condition, temperature, changing router demand and automatic shutdown thresholds. Small AC loads can be disproportionately affected by inverter overhead. Measure the combined load where possible and conduct a timed test without disconnecting any safety-critical service.
A UPS rating in volt-amperes or VA describes output capability, not stored energy. It cannot be converted directly into hours without information about the battery and the manufacturer’s runtime curve. Choose a unit by its supported wattage and published runtime at a load close to your own.
Use mobile data as the independent fallback
If the mobile network remains available, a smartphone can share its data connection with a laptop or tablet through a Wi-Fi hotspot or USB tethering. A dedicated battery-powered hotspot performs the same basic role without tying up the household’s main phone. Check the device setup, password, data allowance and charging arrangement before an emergency.
- Test coverage where the device will be used. A position upstairs or near a window may work better, but keep batteries away from direct sun, moisture and temperature extremes.
- Prefer the strongest stable signal. A phone can use more energy while repeatedly searching for a weak connection.
- Limit connected devices. Disconnect televisions, games consoles, smart speakers, cameras and tablets that do not need internet access.
- Use messaging for routine contact. Text-based services generally place less demand on the phone and network than video calls or streaming.
- Consider network diversity. A low-cost backup SIM can be useful if it operates on a different underlying mobile network from the household’s main phones. Check the provider’s terms, expiry rules and network before relying on it.
The Ofcom Map Your Mobile checker compares predicted 4G and 5G coverage from the four main UK networks. Its results are a planning guide rather than a guarantee during a power cut. Local masts may be affected, capacity can become congested and indoor reception varies by building.
A second brand does not always mean a second network because many mobile providers use one of the four main operators. Check the underlying network when buying a backup SIM. Test it periodically and keep enough credit or an active allowance to use it when required.
Reduce data use and preserve device batteries
- Enable low-power and data-saving modes on phones, tablets and laptops.
- Reduce screen brightness and shorten the screen timeout.
- Pause operating-system updates, cloud backups, photo synchronisation and large downloads.
- Avoid streaming video, online gaming and long video calls unless they are necessary.
- Download a small amount of essential information, then disconnect until the next planned check.
- Switch off Bluetooth, location sharing and background activity that is not needed. Leave mobile reception available if you are waiting for calls or official alerts.
- Charge one priority phone before less important devices.
- Use a separate torch instead of the phone’s light.
The GOV.UK Prepare phone and broadband outage guidance recommends using devices sparingly, keeping paper copies of important numbers and downloading maps for offline use. A phone’s GPS may continue to determine location without mobile service, but a map application may not show useful routes unless its maps were downloaded in advance.
Digital landlines and emergency calls need a separate plan
Many UK landlines now operate through the broadband router. A digital landline normally stops when the router, fibre terminal or broadband service loses power. A familiar corded handset does not overcome this if the call service itself is digital. Cordless phone bases also need electricity.
Ofcom’s digital-landline guidance says customers who depend on their landline and have neither a working mobile phone nor reliable mobile signal must be offered a free backup solution by their provider. It must support emergency contact for at least one hour, although some provider solutions last longer. Tell the provider about the need rather than assuming the correct equipment will be supplied automatically.
If a mobile network is available, a 999 call can use another mobile network when the caller’s own network is unavailable. This does not create signal where no network can be reached. Try 999 or 112 in a life-threatening emergency, keep the call concise and follow the operator’s instructions.
Wi-Fi Calling may allow ordinary mobile calls when the mobile network is unavailable but powered broadband still works. Enable and test it in advance because support depends on the phone, mobile provider and account. Do not make Wi-Fi Calling the household’s only emergency arrangement without checking the provider’s current emergency-call information.
Telecare and connected medical equipment
A personal alarm, health pendant, diabetes sensor or other connected device may depend on mains power, broadband, a digital landline or a mobile network. Ask the device supplier and communications provider what happens during both a power cut and a network outage. Confirm the battery duration, warning signals, test procedure and fallback contact method. A general router backup should not be treated as a substitute for an approved clinical or care plan.
Plan for complete communications failure
In a widespread or prolonged incident, fixed broadband, mobile data and landline services may all become unavailable. Prepare basic offline alternatives rather than spending the last battery capacity repeatedly searching for a connection.
- Keep a paper list of family, medical, school, utility and neighbour contact details.
- Write down 105 for power cuts in England, Scotland and Wales and 03457 643643 for Northern Ireland.
- Keep a battery or wind-up radio and a written list of useful local and national frequencies.
- Download offline maps and keep essential travel details on paper.
- Agree a local meeting point and an out-of-area family contact.
- Arrange an in-person check for anyone who lives alone or relies on connected care equipment.
- Keep some cash available for situations where card terminals or banking services are unavailable.
If mobile data is unavailable but travel is safe, public Wi-Fi at an unaffected library, community centre, transport hub or business may provide temporary access. Confirm that the venue is open before making a special journey where possible. Treat an unfamiliar public network cautiously: check its name with staff, avoid sensitive financial activity and do not install unexpected software or certificates.
Use batteries and generators safely
- Use batteries, cables and adaptors only for purposes approved by their manufacturers.
- Keep power banks and power stations uncovered, dry and away from direct sunlight or other heat sources.
- Stop using a battery that is swollen, damaged, leaking, sparking, smoking, unusually hot or producing an unusual smell.
- Do not overload a UPS or portable power station, and do not exceed the rating of any outlet or extension lead.
- Do not connect a portable power station or generator to a wall socket to energise household wiring.
- Never use a petrol or diesel generator indoors or in an enclosed space. Its exhaust contains carbon monoxide, which can kill.
Electrical Safety First’s power-bank guidance advises using the manufacturer’s cables, keeping batteries ventilated while charging and unplugging them after charging rather than leaving them on prolonged charge when not in use. It also warns that most portable battery packs do not support charging and discharging at the same time.
Test the internet backup before an outage
A controlled test reveals missing equipment, incompatible cables and unrealistic runtime estimates. Charge the backup fully, note the normal status lights, disconnect its mains input as instructed and confirm that internet access continues. Test the mobile hotspot and backup SIM separately. Restore mains power before the battery becomes deeply discharged.
Repeat the test at least twice a year and after changing the router, broadband technology, battery or mobile provider. Check for battery recalls, damage and reduced runtime. Provider-supplied backup equipment may have its own test and replacement schedule, which should take precedence.
Internet access during a power cut checklist
- Identify the router, ONT, modem and other equipment required for the connection.
- Measure or verify the combined wattage of the essential equipment.
- Choose a compatible UPS, provider battery or portable power station with enough runtime.
- Keep charged power banks for phones and USB-powered hotspots.
- Test phone tethering and record the hotspot password.
- Consider a backup SIM that uses a different underlying mobile network.
- Enable low-power and data-saving settings before an outage.
- Download maps and keep important contact details on paper.
- Ask the landline and telecare providers about approved power-cut arrangements.
- Test the complete plan at least twice a year.
Power-cut internet resources
- GOV.UK Prepare phone and broadband outage guidance covers mobile alternatives, Wi-Fi Calling, vulnerable people, offline maps, radios and conserving device batteries.
- GOV.UK Prepare power-cut guidance explains reporting, communications risks, emergency calls, device safety and household preparation.
- Ofcom digital-landline guidance explains why digital phone services need mains power and when a provider must offer a free emergency backup solution.
- Ofcom Map Your Mobile compares predicted indoor and outdoor coverage across the four main UK mobile networks.
- Ofcom’s broadband and mobile checker guidance explains what the coverage tools can and cannot show.
- Electrical Safety First power-bank guidance covers buying, charging, damage, heat, safe cables and recycling.
- BT battery-backup instructions provide one provider-specific example of powering both a broadband hub and a separate full-fibre ONT.
