PowerGuide

How Much Battery Storage Do I Need?

By Rob Hammond · Updated September 2026 · How we score

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The goal isn’t to store all your electricity: it’s to store enough to avoid buying at peak prices. Here’s how to land on a sensible number.

Step 1: Know your daily usage

Check a recent bill or smart meter for your average daily kWh. For reference, Ofgem’s 2026 typical domestic consumption values for a multi-rate (time-of-use) household are 1,900kWh a year at the low end, 3,400kWh medium and 6,100kWh high, or about 5.2, 9.3 and 16.7kWh a day. An EV or electric heating pushes you up a band.

Step 2: Estimate your peak-hour share

How much of that do you use outside the cheap overnight window? Ofgem’s own Economy 7 split puts it at 58% peak / 42% off-peak. Electricity you already use inside the cheap window is billed at the off-peak rate whether you own a battery or not, so it is not worth storing.

Step 3: Size to the shiftable load

Apply that split to your daily usage, because that is the number the battery has to hold. On Ofgem’s values, the medium household shifts about 5.4kWh a day and the high-use household about 9.7kWh. A little headroom for winter is sensible; doubling it is not, because capacity you never discharge is capital doing nothing. That is why a 13.5kWh all-in-one is more than twice what a medium household’s arithmetic supports. See the worked payback.

Try it with your own daily usage:

Ofgem multi-rate typical values: low 5.2, medium 9.3, high 16.7 kWh a day.

Shiftable load
5.4 kWh/day
Suggested usable capacity
6.5 kWh
Est. annual saving
£342
Hardware-only payback
14.6 yrs
Installation is extra. Compare with the warranty length.

Off-peak default is Intelligent Octopus Go (23:30–05:30), which needs a compatible EV or charger. Enter a postcode for your region's rates.

With solar vs without

  • With solar: also size for storing daytime surplus to use in the evening, so you may want a little more capacity.
  • Without solar: size purely for off-peak arbitrage, because there’s no point storing more than you can charge in the cheap overnight window. A 6-hour overnight window on a 3.6kW inverter comfortably fills a typical ~11kWh battery.

Don’t forget power (kW)

Capacity (kWh) sets how long it runs; power (kW) sets how much it can deliver at once. For whole-home backup you want higher power. See our all-in-one batteries, where models like the Powerwall 3 lead on output.

FAQs

What size battery for a typical UK home?

Size it to the electricity you use outside your cheap window, not to your whole day. On Ofgem's 2026 multi-rate consumption values and its 58% peak / 42% off-peak Economy 7 split, a medium 3,400kWh household shifts about 5.4kWh a day and a high-use 6,100kWh household about 9.7kWh, so most homes need less capacity than the 13kWh+ units they are usually shown.

Can a battery be too big?

Yes. If you can't charge and discharge it fully each day, the extra capacity sits idle and slows your payback. Match capacity to what you actually shift off peak.

Related products

GivEnergy · 13.5kWh

GivEnergy All in One

Integrated battery, inverter and gateway in one cabinet, with whole-home backup. A strong fit for storage on a single unit, but check warranty support given GivEnergy's recent administration.

B4.2 ~£4,999
Specs & review

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