Yes, a home battery can power some or all of a house during a power cut, but only if the system has been designed and installed for backup. Many standard grid-connected batteries switch off when the mains supply fails. Having a battery at home does not, by itself, mean you have backup power.
The Energy Saving Trust says a battery normally needs additional equipment and configuration to supply power during an outage. A Distribution Network Operator also explains that batteries usually switch off during a power cut unless they have a backup or island-mode arrangement. See our guide to solar panels during a power cut for more on why grid-connected systems stop operating.
Why a standard home battery may switch off
A typical home battery works while connected to the public electricity network. When the network supply fails, its inverter and controls may stop supplying the house. This is a safety measure: equipment must not send electricity back onto network cables while engineers may be working on them.
For a battery to provide power independently, the installation needs a way to isolate the home from the grid and operate in island mode. The battery and associated inverter or backup equipment must support that operation, and the system must be wired and commissioned for it.
The specific equipment and system design vary. Check the battery and inverter manuals, and ask the installer to confirm in writing whether your system can operate during an outage. Do not rely on a product description that only says the battery stores electricity or reduces bills.
Will it power the whole house?
Some backup systems supply selected circuits, while others can support more of the home. The answer depends on the installed equipment, how the house is wired, the battery’s available energy and the inverter’s power output. “Whole-house backup” still has limits: it does not mean every appliance can run at once.
| Backup arrangement | What may stay on | What to confirm |
|---|---|---|
| Selected-circuit backup | Only the circuits included in the backup design, such as chosen lights, sockets or equipment. | Which circuits are connected to backup and which will switch off. |
| Whole-house backup | A wider range of household circuits, if the system is designed to support them. | The battery and inverter output, likely high-demand loads and any limits on appliances running together. |
| Grid-connected battery without backup mode | Usually no household circuits during a grid outage. | Whether separate backup equipment and electrical work would be needed. |
High-demand appliances such as an electric shower, oven, immersion heater, EV charger or heat pump can exceed a backup system’s output. Motors and compressors may also need extra power when starting. Ask the installer to check the actual loads you want to run rather than assuming they will work because the battery has a large capacity.
How long could a home battery last?
Battery capacity, measured in kilowatt-hours (kWh), affects how long it can supply energy. Inverter output, measured in kilowatts (kW), limits how much power it can provide at a given moment. Both figures matter: capacity affects duration, while output affects which equipment can run together.
A rough planning calculation is:
Approximate runtime in hours = usable battery capacity in kWh ÷ average backed-up load in kW
For example, if 4 kWh is available to the backed-up circuits and their average demand is 0.8 kW, the simple calculation gives five hours. This is an illustration, not a runtime promise. It does not allow for conversion losses, a battery reserve, changing demand or appliances that briefly draw more power when starting.
Check the system’s usable capacity during backup, not only its headline capacity. If the battery normally discharges to reduce bills, ask whether it can keep a reserve for outages and how that reserve affects everyday use. The UK Prepared home battery size calculator and backup battery runtime calculator can help you prepare estimates to discuss with an installer.
Can solar panels recharge the battery during an outage?
Sometimes. Solar panels can recharge a home battery during a power cut only if the system is designed to keep the relevant solar equipment operating while isolated from the grid. A battery that provides backup does not automatically mean that the panels will also work or recharge it.
Ask the installer what happens if the battery runs low overnight, whether the panels can restart the system in the morning and whether they can charge the battery while supplying backed-up circuits. These details matter if you want support beyond the first few hours of an outage.
Questions to ask before relying on your battery
Ask the installer or manufacturer for specific answers about your equipment and home:
- Is this exact battery and inverter model configured for power-cut backup?
- Which circuits will remain available, and which will be disconnected?
- Does backup start automatically, or is there a user procedure to follow?
- What are the continuous and starting power limits in backup mode?
- How much usable battery energy will be available, and can a reserve be kept for outages?
- Can the solar panels recharge the battery while the home is isolated from the grid?
- What should happen if the battery becomes empty, and how is the system returned to normal operation when mains power comes back?
- Has the installation been notified to the local network operator, and have any required approvals been obtained?
If you are considering a new system or changing an existing one, use a competent installer to assess the wiring, protection and network requirements. GOV.UK explains the registration and approval process for home energy devices in England, Scotland and Wales. Ask your installer to confirm the process that applies to your property and keep the relevant commissioning and handover documents.
A fixed battery must be located and installed with safety in mind. PAS 63100:2024 covers protection against fire for battery energy storage systems in dwellings, including installation locations and fault management. Ask the installer to explain how the proposed location and design address the requirements that apply.
If you rent or live in a flat or shared building, get written permission from the landlord, freeholder or building manager before commissioning work. The property, lease and shared-building arrangements may affect whether a fixed system can be installed and where it can go.
If someone relies on powered medical equipment
Do not rely on a home battery for medical equipment until the care team and equipment manufacturer have confirmed that the proposed backup supply is suitable and can provide the required duration. Make a power-cut plan with the care team and equipment supplier as well.
In Great Britain, people who need extra support can contact their supplier and network operator about joining the Priority Services Register. In Northern Ireland, the equivalent support registers are called Customer Care Registers. The UK Government’s power-cut guidance explains the support and planning advice for people with additional needs.
For a broader comparison of fixed batteries with other household backup options, see the UK Prepared guide to backup power for a UK home.
Home battery power-cut resources
- The Energy Saving Trust’s solar power fact check explains why solar and battery systems normally need additional equipment and configuration to supply power during an outage.
- SSEN’s planned power-cut guidance explains how batteries behave during outages on its network and describes backup or island-mode systems.
- GOV.UK’s guidance on registering home energy devices covers DNO notification, approval routes and installation documentation in England, Scotland and Wales.
- BSI’s PAS 63100 overview describes the domestic battery fire-protection specification and its coverage of installation location and fault management.
- Ofgem’s Priority Services Register guidance explains how to contact your supplier or network operator and who may be eligible for additional support.
- The UK Government’s power-cut advice includes practical preparation and guidance for households with medical or other additional needs.
