How to Keep Your Internet Working During a Power Cut
Last reviewed: 20 August 2026
Quick answer: You can often keep your home internet working during a power cut by providing backup electricity to the networking equipment inside your property — usually the router and, for full-fibre broadband, the optical network terminal (ONT). A small UPS, suitable DC backup battery or portable power station can do this.
However, keeping your own equipment powered does not guarantee the internet will remain available. Broadband-provider infrastructure and mobile networks can also be affected by a widespread or prolonged power cut.
Why does Wi-Fi stop during a power cut?
Wi-Fi itself is simply the local wireless connection between your devices and your router. Your router still needs electricity. When mains power disappears, the router shuts down unless it has a backup supply.
With full-fibre broadband you may also have an ONT — a small powered box where the fibre connection enters the property. Keeping only the router powered while the ONT is off will not restore internet access.
Step 1: work out what equipment actually needs power
Look at your broadband setup and identify everything between the incoming connection and your devices.
A typical full-fibre setup may include:
- An optical network terminal (ONT).
- A Wi-Fi router.
- Optional mesh Wi-Fi nodes.
- Optional Ethernet switches.
- A digital/VoIP landline connected through the router.
For emergency use you may need only the ONT and main router. Turning off unnecessary mesh nodes and switches reduces energy consumption and extends battery runtime.
Option 1: a conventional UPS
A UPS — uninterruptible power supply — sits between the wall socket and your equipment. If the mains fails, it switches to its internal battery automatically.
This is attractive for routers because:
- The load is small.
- Automatic switchover is convenient.
- The equipment can remain permanently connected.
- A modest battery may provide useful runtime.
When comparing a UPS, look for expected runtime at a low load rather than buying on the largest VA number alone.
Option 2: a DC router UPS
Many routers and ONTs actually run on low-voltage DC supplied by a mains adapter. A correctly specified DC backup unit can avoid converting battery power to AC and then back to DC, potentially improving efficiency.
But compatibility is critical. Voltage, current capability, connector size and polarity must all be correct. Do not connect a random battery cable to networking equipment because the plug appears to fit.
Option 3: a portable power station
A portable power station is more versatile than a small UPS because it can also run laptops, lighting, phone chargers and other essential electronics.
For networking equipment, the total load may be only a few tens of watts. That means a medium-size power station can potentially run a router and ONT for many hours.
For example, a 500Wh station with roughly 425Wh of usable energy supplying a 20W networking load would have a rough theoretical runtime of about 21 hours. Actual runtime varies with inverter efficiency, standby consumption and the specific equipment.
If you want one battery for several emergency loads, see our portable power station sizing guide and home-backup guide.
Can a normal phone power bank run a router?
Sometimes. USB-C PD power banks can supply several voltages, and properly specified adapters exist for some routers. But this is not a universal plug-and-play solution.
If you want a power bank primarily for phones and emergency communications, our power-bank guide explains the useful features to compare.
Will fibre broadband still work if your router has backup power?
Possibly, but not always. Fibre infrastructure outside the property may have its own resilience, yet a widespread or prolonged outage can affect upstream equipment.
The point of powering your router and ONT is to remove the failure inside your own home. It cannot guarantee that every part of the provider’s network remains operational.
What about digital landlines?
This is increasingly important in the UK. Ofcom explains that a digital landline connected through a broadband router will not work in a power cut unless there is backup power.
Ofcom also says that if you depend on your landline — for example because you cannot use a mobile phone or do not have mobile signal at home — your provider must make sure you can contact the emergency services during a power cut. A solution might involve battery backup or another appropriate means.
If this applies to someone in your household, contact the communications provider before an outage rather than assuming a retail UPS alone solves the issue.
What about telecare, alarms and medical devices?
Some telecare systems, personal alarms, fire alarms and burglar alarms may depend on communications equipment. Ofcom recommends telling your provider about devices that rely on the phone line because they may need to be replaced or reconfigured as networks move to digital technology.
For medical or care equipment, follow the provider’s and healthcare professional’s specific continuity guidance. Do not substitute a DIY battery arrangement for an approved backup plan.
How to make a router battery last longer
- Power only the main router and required ONT.
- Turn off optional mesh nodes.
- Disconnect unnecessary Ethernet switches or smart-home hubs.
- Use efficient DC outputs where safely supported by the equipment.
- Avoid powering high-wattage appliances from the same small battery.
- Reduce unnecessary device use if the outage may last for hours.
Have a second communications route
Even an excellent router backup cannot control the wider network. Keep a charged mobile phone and power bank available. During a major event, text messages may be more practical than long calls if networks are congested.
A battery or wind-up radio is also useful when broadband and mobile services are unreliable. See our emergency radio guide.
Test the setup before you need it
Do not wait for a real power cut to discover that the ONT was not connected to the UPS or that the battery lasts only 45 minutes.
- Identify the router and ONT.
- Connect them to the planned backup supply.
- Temporarily switch off mains power to the backup device according to its instructions.
- Check that Wi-Fi and internet access continue.
- Measure how quickly the battery percentage falls.
- Reconnect mains power and confirm everything recovers normally.
Never interfere with fixed electrical wiring to perform this test.
A simple home internet power-cut kit
- UPS or correctly specified backup battery for the router/ONT.
- Charged phone power bank.
- Short spare phone charging cable.
- Printed emergency and provider contact numbers.
- Battery radio.
- Offline copies of critical documents and addresses.
Frequently asked questions
How long will a UPS run a Wi-Fi router?
It depends on the battery capacity and total load. Routers and ONTs are relatively low-power devices, so a suitably sized UPS can provide meaningful runtime. Use the manufacturer’s runtime chart at a load close to your actual equipment.
Will my landline work in a power cut?
A modern digital/VoIP landline normally depends on powered broadband equipment. Without backup power it may stop. Ofcom requires providers to support access to emergency services for customers who depend on their landline, so contact your provider if this applies to you.
Can I use my laptop as a router battery?
Usually not directly. A laptop can provide phone charging and sometimes act as a hotspot if it has another internet connection, but it is not normally designed to power a broadband router.
Will mobile data work during a power cut?
Often it will initially, but mobile masts can lose power or become congested during a widespread outage. Treat mobile data as a backup route, not a guarantee.
Bottom line
Keeping home internet alive during a power cut is usually a low-energy problem. Identify the router and ONT, provide them with compatible backup power, reduce unnecessary networking loads and test the setup in advance. Then keep a charged mobile phone and offline information as a fallback in case the provider’s wider network also fails.
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