Do home batteries pay for themselves in the UK without solar?

Usually not within the warranty. On a 3,600 kWh home with a 9.5 kWh battery costing £7,500, charging overnight and discharging by day saves about £520 in year one, falling as the battery degrades. That is £4675 over 10 years against £7,500 spent, putting break-even around year 18. The battery would need to cost under about £4,675 to pay back inside its warranty.

Why do battery savings estimates vary so much?

Because most of them model the wrong thing. The common approach multiplies battery capacity by the gap between cheap and expensive rates, which ignores three real costs: the time-of-use day rate is usually higher than the flat rate you were paying, so every unit the battery cannot cover costs more than before; charging is lossy, so you buy more than you get back; and the inverter draws power continuously. Together those can halve the apparent saving.

Is a bigger battery better?

Only up to a point, and that point arrives sooner than most quotes assume. A battery cannot discharge electricity your home will not use. Once usable capacity exceeds the consumption falling outside the cheap window, extra capacity earns nothing while still costing money. For a typical household a smaller battery often pays back faster than a larger one.

When does a home battery make financial sense?

When the installed cost is low, the price spread is wide, and consumption is high enough to absorb a full discharge every day. Batteries also make sense for reasons that are not financial — backup power during outages, or reducing grid draw at peak times — and those are legitimate reasons to buy one. The case that does not hold up is buying purely as an investment.

Home batteries mostly don’t pay for themselves. Here are the numbers.

Published 14 September 2026. Energy rates verified 14 September 2026 against the current Ofgem cap; battery performance figures from manufacturer datasheets and published measurements.

The pitch is simple enough to be seductive. Electricity costs about 8.63p a unit in the middle of the night and about 30.99p during the day. Buy a battery, fill it at 3am, run the house off it until evening. You are buying at a quarter of the price. How could that not pay?

We built a calculator to answer that properly, and the answer for a typical installation is that it doesn’t — not inside the warranty, anyway. This piece walks through why, because the reasons are more interesting than the conclusion, and because three of them are missing from almost every estimate you will be shown.

The worked example

A home using 3,600 kWh a year — above the UK median, so a favourable case. A 9.5 kWh usable battery, which is a common domestic size. An installed cost of £7,500. No solar panels, no electric car, no heat pump.

Annual cost now, on the price cap	£1149
Annual cost with the battery, on a time-of-use tariff	£629
Saving, year one	£520
Total saved over 10 years, after degradation	£4675
Break-even	around year 18

Five hundred-odd pounds a year is a real saving. It is just not enough, quickly enough, against £7,500 and a 10-year warranty. The battery is guaranteed to hold 80% of its capacity at year 10; it needs to keep working well past year 18 to have been worth buying as an investment.

Why the obvious sum overstates it

Multiply 9.5 kWh by the 22.36p spread by 365 days and you get an appealing number. Three things stand between that number and your bank account.

1. You are switching tariff, not switching on a battery

This is the one nobody models, and it is the most interesting. To get the cheap overnight rate you have to move onto a time-of-use tariff — and that tariff’s day rate is higher than the flat rate you were paying. Octopus Go’s day rate has been running around 3p above Octopus Flexible.

So every daytime unit the battery doesn’t cover now costs you more than it did before you bought anything.

In the example above this barely registers — £5 a year — because a 9.5 kWh battery covers almost all of that home’s daytime demand, so there is very little left on the dearer rate. That is worth being straight about rather than overstating the point.

But change the shape of the problem and it bites hard. Take a larger home using 5,000 kWh a year with a smaller 5 kWh battery. Now the battery leaves a lot of daytime demand uncovered, all of it repriced upward, and the switching penalty is £131 a year — against a total saving of only £208. Well over a third of the gross gain is consumed by the tariff change alone.

That is the case a gross-arbitrage calculation is structurally incapable of seeing, because it only ever looks at the energy that goes through the battery and never at what happened to the rest of the bill. It is also, unfortunately, a common shape: undersized battery, larger house.

2. Charging is lossy, and not by the datasheet amount

Round-trip efficiency is the share of what you put in that you get back out. Tesla quote 89% for the Powerwall 3 — explicitly qualified as “typical solar shifting use case, 25°C, at beginning of life”. A battery in a British garage in February, cycling on grid electricity at part load, meets none of those conditions.

Enphase, to their credit, published real measurements for their own product: 90% nameplate, 85.6% measured over 24 hours, 84.0% over a month, and as low as 62% in a worked example combining part-load operation with idle time. We use 85%. The difference between 89% and 85% is worth about 10% of the answer.

3. The inverter never sleeps

A battery inverter draws power continuously whether or not it is doing anything. Fifteen watts sounds like nothing; around the clock at daytime rates it is £41 a year. That is roughly 8% of the saving, gone before the battery does any work.

The ceiling nobody mentions

There is a hard limit on what a battery can earn, and it is not capacity. It is how much electricity your home actually uses during expensive hours.

About 85% of a typical household’s consumption falls outside a six-hour overnight window — households use very little at 3am. For a median home that is roughly 6 kWh a day. A battery bigger than that cannot discharge the surplus, because there is nothing to discharge it into. Every kWh of capacity beyond the ceiling costs money and earns nothing.

What would make it work

The single biggest lever is what you pay. At £4,675 installed — the point where 10 years of savings cover the cost — this same battery breaks even in year 10.0. That is not a fantasy price, but it is well below a typical quote.

Beyond price, the case improves when:

Your consumption is high. More daytime demand means more for the battery to displace before it hits the ceiling.
The spread is wide and the day rate penalty is small. Intelligent Octopus Go has historically had a day rate much closer to the standard flat rate, which removes most of the switching penalty — though it requires a compatible EV, heat pump or battery to qualify.
You value what the spreadsheet can’t see. Backup during power cuts, or simply using less grid electricity at peak times, are real reasons to buy a battery. They are just not financial ones, and they should be argued on their own terms rather than dressed up as payback.

What we are not saying

Not that batteries are a scam. Not that nobody should buy one. The technology does what it says, the savings are real, and the market prices will keep falling.

What we are saying is that a battery bought purely as an investment, on today’s UK prices and tariffs, mostly does not clear its own cost inside its warranted life — and that the estimates suggesting otherwise usually omit the tariff switch, use datasheet efficiency, and ignore standby draw. Those three omissions all point the same way.

If someone quotes you a payback figure, ask them three questions: what day rate did you assume, what round-trip efficiency, and did you include the inverter’s standing draw. The answers will tell you how much to trust the number.

Common questions

Do home batteries pay for themselves in the UK without solar?: Usually not within the warranty. On a 3,600 kWh home with a 9.5 kWh battery costing £7,500, charging overnight and discharging by day saves about £520 in year one, falling as the battery degrades. That is £4675 over 10 years against £7,500 spent, putting break-even around year 18. The battery would need to cost under about £4,675 to pay back inside its warranty.
Why do battery savings estimates vary so much?: Because most of them model the wrong thing. The common approach multiplies battery capacity by the gap between cheap and expensive rates, which ignores three real costs: the time-of-use day rate is usually higher than the flat rate you were paying, so every unit the battery cannot cover costs more than before; charging is lossy, so you buy more than you get back; and the inverter draws power continuously. Together those can halve the apparent saving.
Is a bigger battery better?: Only up to a point, and that point arrives sooner than most quotes assume. A battery cannot discharge electricity your home will not use. Once usable capacity exceeds the consumption falling outside the cheap window, extra capacity earns nothing while still costing money. For a typical household a smaller battery often pays back faster than a larger one.
When does a home battery make financial sense?: When the installed cost is low, the price spread is wide, and consumption is high enough to absorb a full discharge every day. Batteries also make sense for reasons that are not financial — backup power during outages, or reducing grid draw at peak times — and those are legitimate reasons to buy one. The case that does not hold up is buying purely as an investment.

Run it on your own numbers

Your consumption, your current tariff and your quote are what decide this, and they are all different from the example above. The battery ROI calculator takes your figures and shows the workings, including how much each of the three hidden costs is taking from you. The methodology sets out every assumption and where it came from.

Every figure on this page is calculated at render time from the current Ofgem price cap and the assumptions documented in the methodology, rather than typed in, so it moves when the underlying rates move. Battery performance figures come from manufacturer datasheets and published measurements, cited in the methodology. Tariff rates quoted for illustration were current when written and change frequently. Spotted an error? Email hello@energycosting.co.uk.