A battery doesn’t need solar panels. It can fill up from the grid when electricity is cheap and run your home when it is expensive. That is the whole business model of a standalone battery, and it is worth understanding its limits before buying one. It cannot sell its power, it depends on a time-of-use tariff, and for most homes the saving is small next to the price.
Fortyeight’s model gives the numbers below. These are modelled homes, so run it on your own meter data to get yours. Not financial advice — a model, so check real quotes.
How a battery without solar makes money
On a flat tariff, a grid-charged battery saves nothing: it buys a kWh at the same price you would have paid anyway, and loses about 10% of it in the round trip. In the model, a battery on Flexible Octopus saved £0 for every household without solar. So everything depends on the gap between cheap and expensive hours, and on how much you use in the expensive ones.
For a London home over the 12 months to 25 October 2026, Agile prices (5% VAT basis) averaged:
| Time of day | Average Agile price, London |
|---|---|
| 02:00–05:00 | 16.5p/kWh |
| 13:00–16:00 | 15.7p/kWh |
| 16:00–19:00 | 35.7p/kWh |
| Whole year | 20.7p/kWh |
A battery charged in the small hours and drained over the 4pm–7pm peak saves about 17p per kWh after losses. The catch is volume. A typical 2,500 kWh home uses only about 1.3 kWh between 16:00 and 19:00, and about 2.9 kWh from 16:00 to 23:00.
Which tariffs you can use
Most battery-friendly tariffs are only open to homes with something else:
- Octopus Go and Intelligent Octopus Go need an electric car. Intelligent Octopus Go’s terms (clause 2.3.1.3) require an EV or plug-in hybrid. A battery on its own does not qualify.
- Cosy Octopus needs a heat pump, electric radiators or an electric boiler.
- Octopus Flux needs solar panels, a battery and an MCS certificate.
So a home with no car, no heat pump and no solar has one battery-friendly Octopus tariff: Agile. The tariff comparison covers each tariff’s windows and rules.
What a standalone battery saves: modelled numbers
The figures below show what the battery adds over the best tariff the same home could join without a battery. All are grid-charged, with no solar.
| Modelled household | Best battery tariff | 5 kWh | 10 kWh | Break-even price, 10 kWh |
|---|---|---|---|---|
| Typical, 2,500 kWh (London) | Agile | £187 | £210 | £1,912 |
| Typical (North Scotland) | Agile | £213 | £241 | £2,194 |
| Home worker, 3,500 kWh (London) | Agile | £228 | £275 | £2,506 |
| EV, 2,700 + 2,000 kWh charging (London) | Intelligent Octopus Go | £334 | £541 | £4,926 |
| Heat pump, 2,700 + 3,500 kWh (London) | Agile | £298 | £384 | £3,495 |
The break-even price is what the battery could cost and still pay back within 10 years, with capacity fading 2% a year. The Energy Saving Trust puts a 5 kWh system at around £4,600. For the typical home, that is more than twice the 5 kWh break-even of £1,701.
There is also a trap in how savings get quoted. The same typical London home saved £163 a year just by switching from Flexible to Agile, with no battery. A quote that compares “battery on Agile” with “your current flat-rate bill” counts that £163 as battery saving. In North Scotland the switch alone saved only £23, because Agile prices there were higher. See the regional Agile figures.
Exports: why the battery can’t sell its power
It is tempting to picture a battery buying at 16p overnight and selling at teatime. On Octopus’s standard export tariffs, it can’t be paid for that.
Octopus’s export terms (version 2.2, 1 November 2024) limit Outgoing and Agile Outgoing to eligible generation: solar, hydro, micro-CHP, wind and anaerobic digestion, certified by MCS, Flexi-Orb or equivalent. Clause 4.5.1(i) excludes payment for exports “not generated by an eligible generation asset, including… batteries”. With no solar, you have no eligible generation at all.
Octopus Flux does pay for battery exports at its 16:00–19:00 peak rate (30.31p in London). But it requires solar panels and an MCS certificate, so it isn’t open to a standalone battery. The practical result: set the battery to supply only your own home, not to export. Exported battery power earns nothing and still costs you the round-trip losses. Export tariffs explained has the full rules.
VAT: 0% for standalone batteries, until 31 March 2027
HMRC’s VAT Notice 708/6 has zero-rated installed energy-saving materials from 1 May 2023 to 31 March 2027. Since 1 February 2024 that has included batteries, including “the installation of a standalone battery for storing electricity from the grid”. Three points:
- The 0% rate applies to batteries installed in a home. A battery bought from a retailer without installation, for example to fit yourself, pays the standard 20%.
- From 1 April 2027 the rate goes to 5%, not back to 20%.
- The relief applies across the UK, including Northern Ireland.
A 5% rise is about £230 on a £4,600 quote. That is worth knowing, but for a typical home the gap between price and break-even is about £2,900. The VAT deadline guide covers timing.
G98 or G99: the network operator still needs to know
Even with no solar, a battery inverter counts as generation, because it can push power into your wiring. The rules depend on the inverter’s continuous rating:
- Up to 16 A per phase (about 3.68 kW single-phase, or 11.04 kW three-phase): G98. Your installer fits the system and sends the network operator a notification (Form B) within 28 days of commissioning.
- Above 16 A per phase: G99. The installer must apply and get the network operator’s acceptance before installation.
A battery with a 3 kW inverter fits G98. A 5 kW inverter on a single-phase supply is above 16 A, so it needs G99, or an export-limiting scheme (G100) agreed with the network operator. Ask the installer which route applies and who handles the paperwork; the installer question sheet includes this.
What about plug-in solar with a battery?
Plug-in (balcony) solar became legal in Great Britain on 27 August 2026. The legal definition covers solar panels up to 800 W connected by a standard plug, and excludes devices designed to charge storage from the grid. In the model, an 800 W south-facing vertical panel saved a typical London home £133 a year on Flexible, and adding a 5 kWh battery on Agile to it added £189. That is no better than the battery alone, because the battery’s job (evening shifting) barely changes. The plug-in solar page has the payback figures and permission pack.
When a battery without solar makes sense
- You have an electric car and can join Intelligent Octopus Go or Go. The night-to-day gap there is up to about 31p.
- You have a heat pump and use a lot of electricity between 16:00 and 19:00.
- You use well above average in the evenings and can buy a battery for close to its break-even price.
For everyone else, switch to Agile first, move what you can out of the 4pm–7pm peak, and look at a battery again when prices fall. Are home batteries worth it has the price-ceiling test to use on any quote.
Model assumptions: Octopus prices fetched 25 October 2026, Agile import prices from 25 October 2025 to 25 October 2026 on a 5% VAT basis (household electricity in Great Britain is zero-rated for VAT from 1 October 2026 to 31 March 2027, so bills in that period are about 4.8% lower); 95% usable capacity; 90% round-trip efficiency; perfect knowledge of the next 36 hours of use. Real controllers forecast less accurately, so treat these as an upper-middle estimate. Fortyeight is not affiliated with Octopus Energy or any installer.