Home battery ROI, without solar

Whether charging a battery on cheap overnight electricity actually pays for itself. Models the full tariff switch, including the costs most calculators leave out.

Verified: 14 September 2026 from Ofgem price cap and published battery performance data
How is this calculated?
First, does any of this apply to you?

Each of these breaks an assumption this model depends on. We’d rather say so than give you a number we don’t believe.

Your home and tariff

Independent calculator. We don’t pass your details to installers. We don’t earn commission from the result. We update underlying rates monthly and source everything from authoritative public data. See the full methodology.

Common questions

Does a home battery pay for itself without solar?
On current UK tariffs, usually not within its warranty. A 9.5 kWh battery at £7,500 charging on a cheap overnight rate saves roughly £500 to £600 a year at first, falling as the battery degrades, which puts break-even somewhere around year 15 against a 10-year warranty. It gets closer at lower installed cost, on a wider price spread, or in a high-consumption home. The single biggest lever is what you pay for the battery.
Why is my saving less than the price spread suggests?
Three reasons most calculators skip. First, moving to a time-of-use tariff also raises the rate you pay on daytime electricity the battery cannot cover — the day rate is typically higher than a standard flat rate. Second, charging is lossy: at 85% round-trip efficiency you buy more kWh than you get back. Third, the inverter draws power continuously whether or not it is doing anything, which is £30 to £50 a year.
What size battery should I get?
A battery cannot discharge electricity your home will not use. Once usable capacity exceeds your daily consumption outside the cheap window, extra capacity earns nothing while still costing you money. For a typical household using 2,500 kWh a year, that ceiling arrives sooner than most quotes assume, and a smaller battery often pays back faster than a larger one.
Is round-trip efficiency really 90%?
Not in practice. Datasheet figures are measured at beginning of life, at 25°C, at favourable power levels. Enphase published measurements for their own product showing 90% nameplate against 85.6% over 24 hours and 84.0% over a month, falling further with part-load operation and idle time. We use 85% as the default and let you change it.