Home › Guides › How a home battery actually works
BatteriesHow a home battery actually works
Strip away the marketing and a home battery does one thing: it moves electricity from a cheap hour to an expensive one. Everything else is detail, and here is the detail.
Updated 4 August 2026 · from the OVO Solar & Battery team
The one job a battery does
Electricity does not cost the same all day. On the July to September 2026 price cap the standard unit rate averages 26.11p per kWh, and in an overnight window it is far lower. The cheapest published windows on 3 August 2026 ran between 6.99p and 9p per kWh, though nearly all of them are sold as electric vehicle tariffs and ask for a compatible car or charge point. The savings figures on this site model a more conservative 13p, which is our assumption rather than a rate anyone is quoting you. A battery lets you buy at the low number and use at the high one.
That is the whole idea, and neither panels nor sunshine are required for it. What a battery needs is a price difference between one part of the day and another, plus a smart meter so your supplier can see when you used what.
It works in January
Solar generation collapses in a British winter. The arbitrage does not. A battery charged overnight at the off peak rate saves you the same amount in December as it does in June, which is why we size it against your usage rather than your roof.
What is actually in the box
A modern home battery is three things bolted together in one weatherproof cabinet, usually somewhere like a garage, a utility room or an outside wall.
- The cells. Almost every current home battery uses lithium iron phosphate, usually written LFP. It runs cooler and is generally considered the safer chemistry for a house than the nickel based cells used in older products.
- The battery management system. The electronics that decide how hard each cell is worked, keep the pack in its temperature range, and stop it being over charged or over drained.
- The power electronics. An inverter or charger that converts between the direct current the cells store and the alternating current your house runs on.
Usable capacity is the number that matters
Manufacturers publish two capacities. The nominal figure is everything in the cells. The usable figure is what you are allowed to take out, because leaving a small reserve in the pack makes it last longer. Some products publish 90% usable depth of discharge, others 100%. Always compare usable to usable. The battery we quote is 5.2 kWh usable, and that is the number our sizing works from.
Charging, storing, discharging
Nothing is free in physics. You lose a little energy every time you convert it. Round trip losses on a home battery run at roughly 6 to 8% where the battery shares a hybrid inverter with the solar, and roughly 8 to 10% where the battery has its own inverter and sits on the AC side. So expect to get back somewhere around 90 to 94% of what you put in.
That sounds like a lot until you look at the price gap it is working against. Losing 8% of a unit bought at the 13p we model costs you about a penny. Avoiding the 26.11p you would otherwise have paid saves you thirteen. The maths survives the losses comfortably, and it survives them by more on a cheaper overnight rate.
A normal day, in four moves
Overnight, it fills up
Your battery pulls from the grid during the off peak window, when the unit rate is at its lowest. You are asleep and nothing else in the house changes.
Morning, it carries the load
Kettle, shower and the school run all land inside a couple of hours, so the house runs off stored electricity bought at the cheap rate rather than importing at the standard one.
Midday, your solar exports
If you have panels, the roof is generating more than the house needs. With OVO's SEG Install Exclusive rate at 20p per kWh, that surplus is worth more sold than stored.
Evening, it does the heavy lifting
Four to nine in the evening is the most expensive block of the day and the busiest one in most homes. The battery covers it.
Why we often export the sunshine instead of storing it
Using a unit of your own solar saves the 26.11p you would have paid to import it, but gives up the 20p you would have earned exporting it, so the net gain is about 6p. Filling the same battery overnight at the 13p rate we model instead saves around 13p a unit while the solar still goes out at the full 20p. The full working is on the strategy page.
We model both of those strategies against your actual meter data on the free 45 minute design call, then set your system to run whichever pays you more.
Get your free quote →What a battery does not do on its own
A standard grid connected battery shuts down in a power cut. That is not a fault, it is a safety rule called anti islanding, and it exists so nobody is working on a dead cable that your house is quietly re energising. Keeping the lights on through an outage needs extra hardware, which we cover in the guide to gateways and whole home backup.
It also will not do much without a smart meter. Time of use tariffs cannot be applied to a meter that only reports one total, so the meter comes before the battery in the running order.
What it costs, and who fits it
Across the UK market, installed battery prices run at roughly £400 to £900 per kWh, which is a wide band because it covers everything from a small retrofit to a large system with backup hardware. Our own figure is published: £2,444 for 5.2 kWh usable, about £470 per usable kWh, fitted and commissioned, and flat across all our system sizes. Full pricing sits on the costs page.
Installations are carried out by the regional partner business that holds the exclusive OVO partnership for your area, backed by the OVO guaranteed 10 year workmanship warranty. Put your postcode into the coverage page and it will tell you which local OVO expert covers you.
Battery storage installed in a home in Great Britain currently attracts 0% VAT. That relief is scheduled to run until 31 March 2027.
Battery basics, answered
Does a home battery need solar panels?
No. A battery earns its money from the gap between off peak and standard electricity prices, and that gap exists whether or not you have a roof full of panels. Solar makes the picture better, because your surplus becomes export income on top. If your roof is shaded, north facing or simply not yours to use, a battery on its own still stacks up. We walk through the arithmetic in our guide to battery storage without solar.
How long does a home battery last?
The cells are rated in cycles, and mainstream products publish figures from around 6,000 upwards. At one full charge and discharge a day, 6,000 cycles is more than 16 years of use, so in practice the time limit on the warranty usually bites before the cycle limit does. Expect a well specified battery to still be doing useful work well past its warranty term, just with slightly less capacity than it started with.
Is a lithium home battery safe?
The chemistry used in almost all current home batteries is lithium iron phosphate, which is more thermally stable than the nickel based cells found in older storage products and in most laptops. Beyond the chemistry, safety comes from the installation: correct siting, correct protection, correct commissioning. That is the part your 10 year OVO workmanship warranty is standing behind.
Do I need a smart meter?
Yes, in practice. Off peak and time of use tariffs depend on half hourly meter readings, and a traditional meter cannot provide them. If you do not have one yet, that is worth sorting before the battery goes in rather than after, and your local OVO expert will flag it on your design call.
Will a battery power my whole house?
It depends what you mean. A 5.2 kWh usable battery comfortably carries a normal home through the evening peak, which is what it is sized to do. Running an entire house at full draw for hours, through a power cut, is a different job that needs both more stored energy and a gateway. See our guide to whole home backup for what that involves.
Can I add a battery to solar panels I already have?
Yes, and it is one of the most common jobs there is. A retrofit battery normally connects on the AC side with its own inverter, so your existing solar inverter stays exactly where it is. We cover the practicalities in adding a battery to existing solar.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- Ofgem, energy price cap 1 July to 30 September 2026, unit rate 26.11p per kWh and 57.19p daily standing charge ofgem.gov.uk
- Round trip efficiency comparison for AC coupled and DC coupled home storage greenreachenergy.co.uk
- Depth of discharge and module specifications for current UK home battery ranges fox-ess.uk
- Anti islanding behaviour of grid tied solar and storage in a power cut viablepower.co.uk
- Installed cost per kWh benchmarks for UK home battery storage, 2026 kilowatts.uk
- Smart meter requirement for time of use tariffs haboenergy.co.uk
- Published overnight off peak rates of 6.99p to 9p per kWh, checked 3 August 2026, most of them conditioned on an electric vehicle or charge point supplier tariff pages
- OVO Solar and Battery published pricing, battery specification and SEG Install Exclusive rates ovosolarandbattery.co.uk
- HMRC zero rate VAT relief on domestic battery storage to 31 March 2027 solarenergyuk.org
Read next
What a gateway does, and when whole home backup is worth it
A full battery is no use in a power cut without a gateway. Here is what one does.
Read the guide →A home battery without solar panels, honestly assessed
A battery with no panels still earns every night. Here is how much, and where it does not stack up.
Read the guide →Cloudy days and north facing roofs, answered honestly
Cloud reduces output, it does not switch it off. North facing depends on pitch more than compass.
Read the guide →