Guides
Which electricity tariff makes a home battery worth it?
A battery does not earn the cheap rate. It earns the gap between the cheap overnight rate and the rate you would otherwise have paid during the day. That gap runs to somewhere between 17p and 20p a unit at the moment. The wider it is, and the longer your cheap window, the more a battery is worth to you.
Bought at the cheap rate, used at the expensive one.
The gap on each unit, between a cheap overnight rate and the daytime rate you would otherwise pay
Overnight rates of roughly 7p to 9p on the cheapest time-of-use tariffs, against daytime rates in the mid to high twenties, across Great Britain and checked 12 September 2026, before charging losses. It is a range because regional variation is wide and because both ends move with each price cap — three times so far this year. Your own gap is what the estimate works out.
We do not sell tariffs and no supplier pays us. We work out whether a battery pays for your house and, if it does, introduce you to an installer. We do not install anything. The installer pays us a percentage of the installed price when the work is finished. You pay the installer directly and never pay us.
The mechanism
What you are buying is the gap, not the rate
You earn the difference between the two rates, not the low rate itself. A battery charged at around 8p overnight and emptied through the following day avoids buying those same units in the mid to high twenties. The 8p is what you pay; the difference is what you keep.
This is why two houses on the same tariff get different answers. A house using most of its electricity between four and nine in the evening converts almost every stored unit at the expensive rate.
A house that is empty all week and uses little until the weekend does not, and a battery earns less there however good the tariff looks.
It also means the size of the gap matters more than the size of the battery. A large battery on a narrow gap is a slow payback. A modest one on a wide gap, emptied every day, is a quick one.
Read from your own bill, not from the size of your house.
The choice
Three window shapes, and what each lets you move
There are three on the market: a six-hour window, a five-hour one, and Economy 7's seven cheaper-but-weaker hours. They differ in how many cheap hours you get, how cheap those hours are, and whether you have to own something in particular to qualify.
| Shape | Cheap window | Overnight rate | Who can get it |
|---|---|---|---|
| Time-of-use, app-controlled | Six hours, 11.30pm to 5.30am, applied to the whole home | Around 7p to 9p | A compatible electric car or charger, controlled through the supplier's app |
| Time-of-use, fixed window | Five hours, 12.30am to 5.30am, applied to the whole home | A little above the controlled version | No app control needed, so it suits kit the supplier cannot talk to |
| Economy 7 | Seven hours overnight, timing set by your meter and region | Around 13p to 15p | Anyone. There is no eligibility test |
The trade is visible in the table. Economy 7 gives you the most hours and the weakest rate, which roughly halves the gap a battery can earn.
The two shorter windows give a much wider gap across fewer hours, so the battery has to charge faster to fill within the window. That constraint sets the capacity and the charging power of the system, and it is where the inverter guide picks the argument up.
The objection
A cheap night comes with a dearer day
It does, and that is the real risk. Suppliers recover the overnight rate during the other eighteen or nineteen hours, so the daytime rate on a time-of-use tariff usually sits above what you would pay on a standard one.
| Rate | When it applies | Hours a day | Per unit |
|---|---|---|---|
| Standard single rate | All day | 24 | Around 26p |
| Time-of-use, overnight | 11.30pm to 5.30am | 6 | Around 7p to 9p |
| Time-of-use, daytime | The remaining hours | 18 | Mid to high twenties |
Half-hourly tariffs, where the price changes every thirty minutes, are a fourth kind. A battery can earn more on one, and less, and it needs managing. We model the three fixed shapes; if you are on a half-hourly tariff already, send us your usage data and we will work from that.
Read the bottom row first. Without a battery, shifting less than you expected means paying that daytime rate on almost everything, and a time-of-use tariff can cost you more than the one you left.
With a battery sized to cover your evening, most of those expensive hours are bought at the overnight rate instead and the dearer day rate applies to very little.
So the tariff and the battery are one decision. Switching to a wide-gap tariff before the battery is installed will usually make your bill worse.
The eligibility
Do you need an electric car?
For the cheapest windows, usually yes. The six-hour rate is built for electric vehicle charging and the supplier generally wants a compatible car or charger on the account.
Several suppliers now offer similar overnight windows without that condition, and the eligibility rules change often enough that it is worth checking on the day rather than trusting an article.
If you have no electric vehicle and no route onto one of the shorter windows, Economy 7 is the fallback and it still beats a flat rate. The gap is narrower, so the arithmetic is tighter. This is one of the cases where our answer is sometimes that the numbers do not work yet.
What to confirm before you switch
- Whether the cheap rate needs a car or charger the supplier can control, or only a smart meter
- Whether the cheap rate covers the whole house or only the car
- What the daytime rate is, not just the overnight one
- What the exit terms are if the window changes
The conditions
What your meter has to do
It has to be a second-generation smart meter reporting your use in half-hourly periods. Without that, the two shorter windows are not available. Economy 7 can run on an older two-rate meter, on the narrower gap described above.
Suppliers fit one at no charge where you do not already have one.
What has to be true before any of this earns money
- A second-generation smart meter, reporting half-hourly
- A tariff available at your postcode, not just nationally
- A battery scheduled to charge inside the window, confirmed at commissioning
The third one is the one that gets missed. The systems we recommend schedule their own charging, but a system left unconfigured quietly buys electricity at the wrong time of day. Ask your installer to show you the schedule running before they leave.
The caveat
Rates move, so treat every number here as dated
Both ends of the gap are set by other people and both move. Two examples from this year.
On 1 April 2026 off-peak rates on the main electric-vehicle time-of-use tariffs fell sharply — by as much as 39% on some — after the November 2025 Budget removed around £150 of levies from household bills and the Energy Company Obligation was scrapped. That widened the gap rather than narrowing it, because the daytime cap fell by less in cash terms. It could as easily have gone the other way.
From 1 October 2026 the price cap rises 4% to £1,723 a year for a typical dual-fuel home. Electricity barely moves — the average standard variable unit rate goes to 26.32p — because the government has taken VAT on domestic electricity from 5% to 0% for the winter. Gas carries the increase. The next announcement is due on 25 November, for January.
Two different VAT changes are running at once and they are easy to confuse. The one above is VAT on the electricity you buy, zero-rated from 1 October 2026 to 31 March 2027. The one below is VAT on the installation itself.
Installation costs carry dates too. Battery storage fitted in a home is currently zero-rated for VAT, including a battery fitted on its own with no solar panels. That relief is scheduled to end on 31 March 2027, after which the rate is set to rise to 5%. Our prices include the 5% by default; if your installation will be completed before 31 March 2027 you can remove it on your estimate and see the difference.
We publish a review date on every guide for this reason, and we pull figures that have gone stale rather than hedging them. If a number here is more than a few months old when you read it, treat it as an illustration of the mechanism rather than as a quote.
The method
Switching, in the right order
Install the battery first, then switch the tariff. Doing it the other way round costs real money for several months.
Check what you actually use, and when
Half-hourly data from your smart meter shows how much of your consumption sits in the expensive hours. That is the number the whole decision rests on, and it is the first thing we read from your bill.
Establish which tariffs your postcode can get
Availability and rates vary by region, and eligibility rules for the cheapest windows change. This is checked at the point of recommendation, not assumed.
Install and commission the battery first
Including its charging schedule. A battery that is not scheduled against the window earns nothing.
Switch the tariff once the battery is running
Switching first means paying the dearer daytime rate with nothing to offset it.
If your tariff later changes its window length — and they do — the battery does not become useless, but the schedule needs changing and the saving moves. That is worth a diary note once a year.
Questions people ask us about this
Do I need solar panels first?
No. A battery on a time-of-use tariff earns the gap between the overnight rate and the daytime one without generating anything. If you already have solar, tell us on the estimate — it changes the arithmetic rather than the answer, and this first estimate assumes none, so your real saving from the battery will be lower.
Can I get a cheap overnight rate without an electric car?
Sometimes. The cheapest six-hour windows are generally tied to a compatible car or charger, though several suppliers offer overnight windows without that condition, and Economy 7 has no eligibility test at all. We check what is actually open to your postcode before recommending anything.
What if the tariff changes after I have installed?
The battery keeps working and the schedule is changed to match the new window. What moves is the saving, up or down. Nobody can promise you a rate years ahead, and anyone who does is telling you something they cannot know.
Does a battery change my standing charge?
No. The standing charge is paid whatever you do, which is why it does not appear in the arithmetic for or against storage. What changes is the price of the units.
Is there ever a case for not switching?
Yes. If very little of your use falls in the expensive hours, or the only tariff open to you has a narrow gap, the daytime premium can outweigh what the battery recovers. We say so when that is what the numbers show.
What would the gap be worth at your house?
Four questions. We work it out against national average time-of-use rates and show you the workings; your bill then settles your own figures.