How much electricity does your home use per day?
It varies widely between households, so use your own figures. Your annual bill shows the total kWh you used last year; divide by 365 for a rough daily average. Homes with electric heating, an EV or a heat pump use significantly more.
Your actual usage is the most important input for sizing. Annual averages can be misleading because usage varies by season, as winter evenings use more electricity than summer. Our UK battery tracker shows what sizes other UK homeowners are installing.
Which tier fits your home?
Work out how many kWh you use outside the cheap window on a typical day. On Octopus Go, for example, the cheap window is 00:30 to 05:30, so that is everything you use from 05:30 to 00:30.
- About 5 kWh or less: a 5 kWh battery can cover it.
- More than 5 kWh: a 5 kWh battery covers part of it and you still buy the rest at the higher rate. A larger battery covers more, but only pays off if you use the extra capacity every day.
Habo's 5 kWh EcoFlow STREAM is from £2,499 fully installed. On Octopus Go it saves up to about £420 to £490 a year in the best case, assuming it does one full cycle a day and all of it replaces day-rate electricity (see how we worked it out). If you use less than 5 kWh outside the cheap window, you will save less.
Does battery size affect savings?
Yes, but bigger is not always better. An oversized battery leaves unused capacity sitting idle every day, increasing your upfront cost without proportional savings. An undersized battery means you still draw from the grid at higher rates. The ideal battery covers your use outside the cheap window without significant excess.
The oversizing trap
A common mistake is buying the largest battery available on the assumption that more storage equals more savings. If your battery is bigger than the electricity you use outside the cheap window, the extra capacity costs you money upfront but generates no additional savings. For more on how sizing affects value, see our guide to battery cost per kWh.
The exception is if you plan to add solar panels later. In that case, a larger battery can store more surplus solar generation during the day. But for a grid-only setup, match the battery to your actual usage.
How to check your actual electricity usage
The most reliable way to size a battery is to look at your real consumption data. Here is how to find it:
Smart meter in-home display: Many smart meters show your daily consumption. Look at a typical weekday, particularly the evening.
Energy supplier app: Many suppliers provide half-hourly usage data through their app or online account. Look at your average daily use outside the cheap window over the last month.
Annual bill: Your bill shows the total kWh you used over the year. Divide by 365 to get a rough daily average. This is less precise but gives a starting point.
Usable capacity
Not all of a battery's stated capacity may be usable. When comparing batteries, check the usable capacity on the spec sheet, not just the total capacity, and compare prices per usable kWh.
Battery sizing with solar panels
If you have solar panels, battery sizing works differently. The battery needs to capture surplus solar generation during the day and release it in the evening. The right size depends on how much excess solar your panels produce, which depends on panel capacity, roof orientation and the season. Ask your installer for an estimate of your surplus generation in summer and winter.
What Habo recommends
Habo currently sells a 5 kWh EcoFlow STREAM from £2,499 fully installed. It is electrician-wired to your consumer unit under G98 and BS 7671, not a plug-in socket battery. Savings are up to about £420 to £490 a year on Octopus Go in the best case, one full cycle a day, with a best-case payback of about 5.1 to 6.0 years (see how we worked it out). If you use much more than 5 kWh outside the cheap window, it will cover only part of it. Habo's current product is 5 kWh.
If you live in a smaller property or have lower usage, see our guide to batteries for flats. If you charge an EV at home or have a heat pump, you may need a larger battery to cover your use. Habo does not currently sell larger kits.
Not sure what size you need?
Try our savings calculator to estimate your annual savings, or read our complete guide to home battery storage systems. Habo sells a 5 kWh EcoFlow STREAM from £2,499 fully installed. Join the waitlist, nothing to pay today.
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