The right home battery size depends on your house, your heating, your tariff, and whether you have an EV. This guide gives a quick-answer table for the typical setups, a sizing formula you can run yourself, and worked examples for the five most common UK homes.
Indicative sizes for properties on a time-of-use tariff (e.g. Octopus Cosy / Flux / Go). Sizes assume charge-overnight-and-cover-the-day strategy. Without a time-of-use tariff, you can size slightly smaller.
| Property | Heating | EV? | Battery size |
|---|---|---|---|
| 1-bed flat | Electric / gas | No | 5 – 8 kWh |
| 2-bed flat or small terrace | Gas | No | 5 – 10 kWh |
| 3-bed semi | Gas | No | 10 – 13 kWh |
| 3-bed semi | Gas | Yes | 13 – 17 kWh |
| 4-bed detached | Gas | No | 13 – 17 kWh |
| 4-bed detached | Gas | Yes | 15 – 20 kWh |
| 4-bed detached | Heat pump | No | 17 – 20 kWh |
| 4-bed detached | Heat pump | Yes | 17 – 25 kWh |
| 5-bed+ / large house | Heat pump | Yes | 20 – 30 kWh |
The Energy2 V3 Black is 17 kWh per module — sized to cover the entire 4-bed range from baseline through heat-pump + EV. For larger homes the V3 stacks modularly. For 1- and 2-bed flats, smaller systems from other manufacturers are usually a better fit.
Two numbers from your annual electricity bill, one multiplier. Gives you a target battery capacity within a few kWh of what a proper survey would recommend.
Worked example: a 4-bed home using 4,200 kWh/year. Daily average = 11.5 kWh. Target capacity = 11.5 × 1.3 = ~15 kWh. The 17 kWh V3 Black covers this comfortably with headroom for cold-snap days.
This formula works for most homes. It under-counts for households with electric heating or heat pumps (where the heating load skews seasonal); for those, add 5-8 kWh on top.
Annual usage: 2,800 kWh. Daily average: 7.7 kWh. Formula target: 10 kWh. Recommendation: 8-10 kWh. The 17 kWh V3 is bigger than necessary here — a smaller system pays back faster. (We're honest about this: not every house is a V3 house.)
Annual usage: 3,500 kWh. Daily average: 9.6 kWh. Formula target: 12.5 kWh. Recommendation: 10-13 kWh. The V3 fits comfortably with headroom for upgrades (EV or heat pump later). Payback typically 6-8 years on a time-of-use tariff.
Annual usage: 4,200 kWh household + ~2,000 kWh EV. EV typically charges directly on an EV tariff (Intelligent Go at 8p/kWh) — so battery doesn't need to cover it. Daily household average: 11.5 kWh. Formula target: 15 kWh. Recommendation: 13-17 kWh. V3 covers comfortably.
Annual usage: 4,200 kWh household + 4,500 kWh heat pump (varies hugely with COP and insulation). Daily winter usage can hit 35-40 kWh during a cold week. Recommendation: 17-20 kWh. The V3 sits at the lower end. Some heat-pump households add a second V3 module for cold-snap resilience; most don't need to.
Annual usage: 6,000+ kWh household + 6,000+ kWh heat pump + 4,000+ kWh EV (less if EVs charge on dedicated tariff). Daily winter peak can approach 60 kWh. Recommendation: 25-34 kWh. Typically two V3 modules (34 kWh total) or one V3 plus a top-up.
A common pattern in UK home battery installs from 2020-2023 was 5 kWh systems sized to a small flat's daily usage. They sold well — small price tag, small payback claim. Then the customer added a heat pump, or got an EV, or moved up tariffs to time-of-use, and the battery was suddenly half the size they needed.
Battery storage is one of those rare purchases where slightly-too-big is usually better than slightly-too-small. The extra capacity is dormant, not wasted — it absorbs solar surges, covers cold-snap demand, and doesn't constrain your tariff strategy. Whereas an undersized battery caps your savings ceiling permanently.
Our standard advice for a UK 4-bed: don't go below 13 kWh. The V3's 17 kWh is sized to be the right minimum for most 4-beds without forcing modular stacking later. For smaller homes, we'll often recommend a different manufacturer rather than try to fit a V3 where it's overkill.
See our tariff guide for which Octopus tariff suits your household, and how each affects optimal battery size.
For a typical 4-bed with gas heating, no EV, no heat pump: 10–13 kWh is enough. Add an EV: 13–17 kWh. Add a heat pump: 15–20 kWh. Add both: 17–25 kWh. Our 17 kWh V3 Black covers the whole 4-bed range from baseline through heat-pump-plus-EV. We size precisely as part of the free survey.
Heat pumps draw 15–30 kWh per day in UK winter conditions depending on size, insulation and outdoor temperature. For a 4-bed home with a heat pump on a time-of-use tariff, 15–20 kWh of battery storage lets you charge during cheap windows and run the heat pump from stored energy through the day. A single 17 kWh V3 fits this scenario well; severe-winter households sometimes add a second module.
EV charging is typically handled directly on a dedicated tariff (e.g. Intelligent Octopus Go at 8p/kWh) using a smart charger — not from the home battery. The home battery covers the household load you're shifting away from the peak window. 13–17 kWh suits most EV-owning 4-beds.
Yes. If your daily usage is 10 kWh and you install a 30 kWh battery, you'll only ever cycle a third of it — the extra capacity sits unused, you pay for what you don't need, and payback extends. Right-sizing matters. Our free survey models your half-hourly usage and recommends a size you'll actually use.
Take your annual electricity use (on your bill), divide by 365, multiply by 1.3. That gives a rough target capacity. A typical UK 4-bed without heat pump or EV sits around 12 kWh/day usage, so 15–17 kWh is the right zone. We refine this with half-hourly smart meter data during the survey.
Yes. V3 modules stack modularly — you can start with one (17 kWh) and add a second later if your usage grows (EV, heat pump, family). Some manufacturers' batteries are sealed at a fixed capacity and can't be expanded. Future-proofing is a deliberate design choice on the V3.
No. UK 0% VAT relief on residential battery installs applies regardless of capacity — 5 kWh or 50 kWh, the rate is the same. Size based on your actual needs, not VAT.
The formula above is a rough guide. A free survey gives you a sizing based on your actual half-hourly usage data — accurate to within a kWh or two.