What we recommend
A battery, sized on your bill, with nothing on the roof.
Bigger than most people are sold, because the homes we advise use more than most. Sometimes nothing at all, because below a certain spend it does not pay. Here is what we recommend, when we say no, and what it costs.
Illustrative figures. The prices and thresholds on this page are worked examples, not confirmed HES pricing. Installed prices are pending — HES is a new business, and prices will be confirmed once our installer partner's rate card is agreed.
A month on electricity. Below that, we tell you not to buy a battery yet.
Below £200 a month a battery takes longer than seven years to pay for itself, and we say so in your estimate before you give us a name. Between £200 and £300 it usually needs an electric car or a hot tub to get there. Seven years is a house rule, applied by the estimator; it moves when prices or tariffs move. Basis: a 20 kWh battery, rates at 1 October 2026.
The recommendation
A home battery on a time-of-use tariff, and no panels
What we recommend is a battery and an inverter, installed inside or against the house, charging in the cheap overnight window and running the house through the expensive hours. Nothing goes on the roof: no panels and no scaffolding, a battery inside or against the house does not normally need planning permission, and the work takes one and a half to three days depending on the size, with your supply off for part of it.
That is deliberate rather than a limitation. The saving comes from the gap between the overnight and daytime rates, which a battery captures on its own. Solar adds to it on the right roof, and if yours is one we will say so — but it is a second decision, not the first.
The roofline stays as it is. The battery sits beside the house.
The size
Bigger than you'd think: 20 to 50 kWh
The size that pays is the size that covers what the house uses between one cheap window and the next. Most batteries sold in Britain are 10 to 14 kWh, which suits a home using 4,000 kWh a year. The homes we advise use two to five times that — an EV, a hot tub, electric heating — so the range starts where the usual range stops.
We're paid by the installer once you go ahead, and a bigger job could be worth more to whoever pays that fee — so you should not take our word for the size alone. Every recommendation shows the arithmetic: what the house used last year, how much of it a given battery can shift, and the payback for each size we considered. The one we recommend is the one where the battery fills most nights and empties most days.
How the inverter is sized against the battery — what it does, and what G98 and G99 mean for your installation.
| Size | Suits a home using | Typically | Installed price |
|---|---|---|---|
| 20 kWh | 8,000 to 11,000 kWh a year | An EV or a hot tub | Pricing pending |
| 30 kWh | 11,000 to 15,000 kWh | An EV and a hot tub | Pricing pending |
| 40 kWh | 15,000 to 20,000 kWh | EV, hot tub, electric heating; three-phase supply only | Pricing pending |
| 50 kWh | Over 20,000 kWh | Two EVs, a heat pump, a pool; three-phase supply only | Pricing pending |
| Nothing | Under 8,000 kWh, or under £200 a month | We say so in the estimate | £0 |
When we say no
Sometimes we recommend nothing
Below £200 a month the estimate says so, before you have given us a name or an email. A battery still works at that spend; it just takes too long to pay for itself, and an adviser who is paid on completion has every reason not to tell you that. Telling you anyway is the whole business.
There are other reasons to say no, and the estimate names them too. No smart meter and no intention of having one. No time-of-use tariff available at the postcode. A fuse board (your consumer unit) that needs replacing first, which the installer will price separately rather than bury in the system cost. Already on an EV or time-of-use tariff: you have the tariff saving already, so the battery has to pay for itself alone, which runs to about seven and a half years. We show that figure rather than the combined one.
Your bill decides it, read properly rather than guessed at.
The process
Estimate, recommendation, survey — in that order
Each step costs you a little more effort and gives you a firmer number back. Nobody comes to the house until there is a priced recommendation you have read.
Your estimate, from four questions
Postcode, monthly spend, whether you charge a car at home, and the big loads in the house. You get a saving and a size, openly approximate, with the assumptions beside it. No contact details until there is a figure to send you.
Your recommendation, from your documents
Send a year of electricity bills and photographs of your meter, your fuse board and where the battery would go. We read your actual consumption, run it against the tariffs at your postcode, and send a priced recommendation — usually within one working day.
The survey, then the install
The installer partner visits to confirm the recommendation rather than upgrade it: where the battery sits, the earthing, the fuse board. The install itself takes one and a half to three days depending on the size, with your supply off for part of it.
A year of bills and three photographs
- A year of electricity bills. An annual statement from your supplier's app is best.
- Your meter. Time-of-use tariffs need a second-generation smart meter (SMETS2).
- Your fuse board, with the cover on; do not unscrew anything.
- Where the battery could go: dry, out of direct sun, not a bedroom or loft, and as near the fuse board as possible.
- An electrical inspection certificate (EICR), if you have one.
A phone photograph is enough for each.
What else it does
The same battery, in a power cut
Wired for it, the battery notices a power cut before you do and carries the house through it — the essentials for a day and a half to two days on a full 20 kWh battery, longer on the bigger ones. It is not the reason to buy, and most homes will barely use it, but it is a modest addition to a battery the bill has already justified.
Keep it for the power cuts — what it takes, what it adds to the price, and who it is for.
The street is dark. The house with the battery is not.
How you pay
You pay the installer. The installer pays us.
You buy the system outright from the installer partner, in the stages the installer sets — normally a deposit on order and the balance on completion. We do not offer finance and we do not take your money at any point.
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. More on how that works.
Questions people ask about the recommendation
Why not the 13.5 kWh battery everyone else sells?
Because it empties by mid-afternoon in the homes we advise, and the rest of the day is bought at the daytime rate. A battery that runs out is a battery that stopped saving. Sizing to the house is the recommendation; the number follows from the bill.
Can I add solar later?
Yes, if the inverter is chosen with it in mind, which is how we specify. Panels then charge the same battery by day, and the overnight charge shrinks to whatever the sun did not cover.
What is the warranty, and what happens if the installer stops trading?
The warranty is the installer partner's, on the battery, the inverter and the work. The terms come with your recommendation so you can read them before anyone visits. Warranty summary to be confirmed with the installer partner. Every installer we work with is MCS-certified, and that certification carries its own complaints and redress route if things go wrong — see how we handle complaints. If you pay any part by credit card, section 75 of the Consumer Credit Act may also make the card provider jointly liable, which is worth raising with them in parallel.
How long does the installation take?
One and a half days for the smaller systems, up to three for the largest. There is no scaffolding and no roof work; the time goes on the fuse board, the inverter and commissioning. Your supply is off for part of it.
What about an EV charger?
If you do not have one, the survey can price one alongside the battery, on the same time-of-use tariff. It is the one addition we would raise unprompted, because it is the load that most changes the size.
Is a battery safe in your home?
The batteries we recommend use the most thermally stable lithium chemistry, and are installed to the British Standard for home batteries, away from escape routes. The detail is below.
Domestic battery fires are rare, but the risk is not zero, and we would rather tell you what it actually depends on than pretend otherwise. It comes down to four things: the battery's chemistry, the quality of the product, the quality of the installation, and where it is sited.
Most modern domestic batteries, including the ones we recommend, use LFP (lithium iron phosphate) cells. LFP is widely used precisely because it is more thermally stable than older lithium chemistries — it is harder to push into the kind of runaway heating that causes a fire. Chemistry is only part of it, though. A compliant installation matters just as much: installers we work with are expected to follow PAS 63100:2024 (the British Standard for installing electrical energy storage systems) and BS 7671 (the UK wiring regulations), which between them cover correct siting, ventilation, separation from escape routes, and the electrical work itself.
Every reputable battery also has its own battery management system — the electronics inside it that continuously monitor temperature, voltage and the condition of individual cells, and that will disconnect or shut the unit down if something moves outside safe limits before a person would ever notice. Reputable, certified products and installers who are actually qualified in battery storage — not just general electrical work — are the two biggest factors in whether all of that functions as intended. Where appropriate, a compliant installation also includes suitable smoke or heat detection near the unit and enough fire separation from the house itself. Poor installation or wiring is where most real risk comes from, not the battery sitting there quietly working.
One thing worth doing on your side: tell your home insurer you're having a battery installed, where your policy requires you to notify them of home improvements or electrical installations.
Do they burst? A cell failing catastrophically enough to rupture or vent is an extreme, low-probability event for a well-made LFP battery, and it is exactly what the battery management system, the installation standards and the manufacturer's own certification are there to guard against at every stage. We are not going to tell you the risk is zero — no piece of electrical equipment in your house is — but a properly selected battery, installed correctly by a competent installer in the right place, is a low-risk piece of equipment, and asking your installer how they meet PAS 63100 and what the battery management system does is a reasonable question to have answered before you go ahead.
Where would the battery actually go?
Inside or against the house — a garage wall, a utility room, a plant room, or an external wall: dry, out of direct sun, not a bedroom or a loft; an unheated or damp outbuilding is usually unsuitable. It goes wherever the cable run back to your fuse board is shortest, since that is the commonest reason an installed price moves after a survey. The survey itself checks wall suitability, temperature, ventilation and access before anything is agreed; nothing about siting is decided from photographs alone.
Can I have one if my house is listed, or in a conservation area?
In most cases, yes for the same reason solar often cannot: nothing goes on the roof, so there is no scaffolding and no planning permission needed for the battery and inverter themselves. Listed building consent is a separate legal regime from planning permission, and whether it applies to a specific installation has not been confirmed — that is settled at the survey, not here.
Is my electricity supply suitable?
A single-phase supply is standard and takes a 20 or 30 kWh system. Above that you need a three-phase supply. The photograph of your fuse board tells us which you have.
What would your own house save?
Four questions. No contact details until there is a figure to send you, and the workings beside it when there is — including when the answer is not yet.