What Appliances Can a Home Battery Run During a Power Cut?
A backup-capable home battery can keep much more than the lights on during a power cut. The real limit is set by two different numbers: how much power the system can supply at one moment and how much usable energy is stored for the outage.
That distinction is why a small Wi-Fi router can run for many hours while a kettle may be easy to run for only a few minutes, and why an electric shower can be a completely different design problem even when the battery has plenty of energy left. kW tells us what can run together; kWh tells us how long it can keep doing it.
At Sustainable Energy Engineering, we ask what you actually want to protect before we promise “whole-house backup”. For many homes, refrigeration, lighting, broadband, heating controls and selected sockets matter far more during a long outage than keeping every high-power appliance available.
What a Home Battery Can Usually Keep Running
- Low-power essentials are normally straightforward. Lighting, broadband equipment, a fridge or freezer, televisions, laptops and heating controls are usually practical priorities on a suitable backup system.
- High-power appliances need a kW check. Kettles, microwaves, ovens, heat pumps, electric showers and EV charging can require much more instantaneous power.
- Runtime depends on kWh. A battery with enough power to start an appliance can still run out quickly if the average backed-up load stays high.
- Startup power can matter. Compressors, pumps and motors may briefly draw more than their normal running power.
- A battery does not automatically provide backup. The inverter, isolation and changeover arrangement must support operation when the public grid is unavailable.
This guide shows you how to think about common household loads, startup power, battery runtime, whole-home versus essential-load backup and solar charging during a power cut.
First Check: Does Your Battery Actually Provide Backup?
Not every home battery keeps supplying electricity when the grid fails. Some systems are installed only for solar self-consumption or tariff savings. When the grid disappears, they shut down with it.
A backup-capable installation needs to detect the grid failure, disconnect the backed-up part of the property safely from the public network, and then create a local supply. Depending on the product, this may use a gateway, system controller, EPS output, automatic changeover arrangement or other dedicated equipment.
That is why the first question is not "how many kWh is the battery?" It is "what has this installation been designed to do when the grid goes off?"
Our earlier guide, What Happens to Solar Panels During a Power Cut? , explains anti-islanding and why ordinary grid-connected solar does not simply carry on powering the house.
The Two Numbers That Decide What You Can Run: kW and kWh
kW: What Can Run Together
Power is the instantaneous limit. A battery can have plenty of stored energy and still be unable to support several high-power appliances at the same time.
kWh: How Long It Can Run
Energy is the fuel tank. Once you know the average backed-up load, usable kWh gives a much clearer picture of likely runtime.
kW Is How Much Power You Can Use at Once
Power is the rate at which your appliances need energy. It is measured in kilowatts (kW). If the backed-up appliances demand more power than the system can provide, the inverter may limit output, disconnect, or require load shedding.
For example, a kettle might draw about 3kW while it is heating. If lights, a fridge and a microwave are already using another 1.5kW, the backup system may briefly need around 4.5kW. A battery with 10kWh of stored energy still cannot support that combination if its backup output is limited to 3.68kW.
kWh Is How Long the Stored Energy Can Last
Energy capacity is measured in kilowatt-hours (kWh). It tells you how much energy is available over time. A low-power load can run for many hours; a high-power load can consume the same battery much more quickly.
Our usable versus nominal battery capacity guide explains which capacity figure matters when you estimate real backup duration.
That formula is only an estimate. Real backup time also changes with battery state of charge, reserve settings, temperature, inverter losses, appliance cycling, solar generation during the outage and any minimum state-of-charge protection.
What Common Appliances Can a Home Battery Run?
The table below gives practical household ranges to help you understand scale. These are not design values . Check the rating plate or manual for your own appliance because similar-looking products can draw very different power.
| Appliance or load | Indicative power | Backup view |
|---|---|---|
| Wi-Fi router / broadband equipment | About 5-20W | Very small load; normally easy to prioritise |
| LED lighting | Roughly 5-15W per lamp | Usually easy to support, especially if only essential rooms are used |
| Laptop and charger | About 30-100W | Normally straightforward |
| Television | About 50-150W | Normally modest, depending on screen size and type |
| Fridge / freezer | Often about 50-200W while running | Usually suitable, but compressor startup power matters |
| Gas boiler controls and circulation pump | Often about 50-200W | Small electrical load, but confirm the boiler and controls are on backed-up circuits |
| Microwave | Often about 1-1.5kW input | Usually possible on a capable system, but adds a large short-term load |
| Kettle | Often about 2-3kW | High instantaneous power but normally used for only a few minutes |
| Washing machine | Can vary from a few hundred watts to around 2kW or more | Heating stage matters; avoid during long outages unless capacity is comfortable |
| Dishwasher | Often about 1-2.5kW during heating | Possible on some systems but not normally an essential outage load |
| Electric oven | Often around 2-3kW | Can use substantial power and energy; system design matters |
| Induction hob | From about 1kW for one low-power zone to several kW with multiple zones | Needs active load management on smaller backup systems |
| Heat pump | Often around 1-5kW electrical input, sometimes more | Highly design-dependent; compressor startup and auxiliary heating need checking |
| 7kW EV charger | Up to about 7.4kW single phase | Usually a poor priority during an outage unless the system is specifically designed for it |
| Electric shower | Commonly about 7-10.5kW | Often excluded from domestic battery backup because of the very high load |
Notice that high power does not always mean high energy . A 3kW kettle used for five minutes consumes only about 0.25kWh. It may be easy on the battery's energy capacity but difficult for a low-power inverter if several other appliances are running at the same time.
The opposite can also happen. A 2kW electric heater is not an extreme instantaneous load for some batteries, but four hours of continuous use would consume about 8kWh before system losses. That can empty a typical home battery quickly.
Why Startup and Surge Power Matter
Some appliances briefly need more power when they start than they use once running. Refrigerators, pumps, compressors and some motor loads are common examples.
A battery datasheet may therefore quote both:
- continuous output: the power it can sustain;
- peak or surge output: higher power it can provide for a short period;
- motor-start capability: sometimes expressed using locked-rotor current or a time-limited peak.
This is one reason we do not size backup by adding only the normal running wattage of each appliance. The system has to survive the moment a compressor or pump starts while other loads are already connected.
Two Current Product Examples Show Why the Exact Battery Matters
Tesla lists Powerwall 3 with 13.5kWh nominal battery energy and UK output configurations up to 11.04kW, depending on local conditions and commissioning. Enphase lists the IQ Battery 5P with FlexPhase at 5.0kWh usable capacity and, in UK single-phase configuration, 3.68kVA continuous output per battery with higher short-duration backup output.
Neither example is "better" from those two numbers alone. One home may need a larger single-unit power capability; another may be better served by a modular system. The point is that batteries with similar jobs can have very different kW-to-kWh relationships .
How Long Will a Home Battery Run Your Appliances?
Runtime depends on the energy that is actually available when the power cut starts. If a 10kWh battery is only 40% charged, you do not have 10kWh waiting for the outage.
Here are three simple illustrative cases using 10kWh of available stored energy and an assumed 90% discharge path efficiency:
| Average backed-up load | Examples | Approximate duration |
|---|---|---|
| 0.35kW | Fridge/freezer, router, a few lights, laptop, heating controls | About 25.7 hours |
| 0.60kW | Essentials plus more lighting, television and occasional short cooking loads averaged over time | About 15 hours |
| 2.0kW | Sustained high electrical demand | About 4.5 hours |
Those are arithmetic examples, not promises. A real system may reserve energy for battery protection, limit output at certain temperatures, receive solar during the outage, or have a different AC efficiency.
If you are deciding between battery capacities, our guides to what size solar battery you need and 5kWh vs 10kWh vs 15kWh batteries explain why capacity should be matched to timed demand rather than chosen from the headline size alone.
Whole-Home Backup vs Essential-Load Backup
Essential-Load Backup
With an essential-load arrangement, selected circuits are kept alive during an outage. Typical priorities might include:
- fridge and freezer;
- internet and communications;
- selected lighting;
- heating controls and pumps where appropriate;
- some socket outlets for phones, laptops and a television.
Heavy loads such as electric showers, EV charging and some cooking circuits can be left outside the backed-up board. This often gives longer runtime and makes the system easier to size around genuine needs.
Whole-Home Backup
Whole-home backup can be very convenient, but it does not remove the power limit. It simply means the backed-up supply covers the whole property rather than a selected set of circuits.
If several large appliances are turned on together, the system still has to supply their combined demand. Some products and installations can manage substantial household loads; others rely on homeowner discipline or automated load control.
Our guide Can Solar Panels Power Your Whole House in the UK? looks at the wider difference between annual energy, instantaneous power and self-sufficiency.
Can Solar Panels Keep Charging the Battery During a Power Cut?
Sometimes, but only when the system has been designed to operate that way while safely isolated from the grid.
In a standard grid-connected solar installation, the inverter normally shuts down when grid conditions disappear. A backup-capable solar-and-battery system can instead form a local microgrid and may allow the solar array to keep supporting the home and recharging the battery.
That can transform backup duration. A battery that might last one night on stored energy alone could continue much longer if useful solar generation returns the next day. But weather, array size, battery state and the system's off-grid charging architecture all matter.
Which Appliances Should You Prioritise in a Long Power Cut?
If the outage could last hours rather than minutes, we would normally protect the loads that preserve safety, communication, food and basic comfort before spending energy on convenience.
- Fridge and freezer: protect food, but avoid opening doors unnecessarily.
- Internet and phone charging: useful for communication and updates.
- Lighting: LED lighting uses relatively little energy.
- Heating controls: a gas boiler may need only a modest amount of electricity for controls and pumps, though the exact system must be checked.
- Medical or accessibility equipment: identify these loads before the system is designed. Do not rely on a general home battery as the sole contingency for life-critical equipment without the dedicated resilience arrangements recommended for that equipment.
- Cooking: use short, lower-energy options where practical instead of running several electric cooking appliances together.
- Delay discretionary heavy loads: EV charging, immersion heating and other high-energy tasks can usually wait until the grid returns.
How We Design Battery Backup Around a Home
We do not start with a promise that "this battery will run everything". We start with a list of what you want to keep running.
Then we check:
- the continuous and peak power of the proposed battery/inverter system;
- the usable battery energy and backup reserve;
- the startup behaviour of motors, pumps and compressors;
- whether the property is single-phase or three-phase;
- which circuits should be backed up;
- how the system isolates from the grid and forms an islanded supply;
- whether solar can continue operating during an outage;
- earthing, protection and changeover requirements;
- battery location and domestic fire-safety requirements;
- the expected runtime under an essentials-only and a normal-living scenario.
That gives you a backup design you can actually understand. It also lets us show the trade-off between using a larger battery, adding more power capability, backing up fewer circuits or simply changing behaviour during a rare long outage.
A Simple Checklist Before You Buy Battery Backup
- Does the quoted installation provide backup, or only battery storage?
- Is the backup whole-home or selected-circuit?
- What is the continuous backup power in kW?
- What peak or motor-start power is available, and for how long?
- How many usable kWh are available during an outage?
- What state-of-charge reserve will be maintained?
- Can solar operate and recharge the battery while islanded?
- What happens if a large appliance exceeds the power limit?
- Can loads be automatically shed or prioritised?
- What runtime does the installer estimate for your actual essential loads?
High Power Does Not Always Mean High Energy
- A kettle may draw around a few kilowatts, but only for a short time, so the total energy used can still be modest.
- An electric heater drawing less power can use far more stored energy if it runs continuously for hours.
- That is why we check both the peak appliance load and the expected duration rather than judging backup from one number.
Want Backup Designed Around the Appliances You Actually Care About?
We can design solar PV with battery storage around your normal energy use and your outage priorities, then explain exactly what is and is not backed up before you buy.
Contact Sustainable Energy Engineering or call 0191 340 7001 .
