Batteries
A home battery without solar: the 18.72p per kWh maths, and the payback question
Last checked: 15 October 2026 · SmartShift UK
A home battery without solar panels can still save money on a tariff with a cheap night rate: charge it overnight, then run the house from it in the day. The saving per kWh is simply the gap between the two rates, minus what is lost in the battery. Whether it pays back depends on the installed price, which only a quote can tell you.
The 18.72p per kWh maths
- Each kWh charged at 7.6p and used instead of 26.32p saves 26.32 − 7.6 = 18.72p, before losses.
- A battery with 5 kWh usable, filled and emptied once a day: 5 × 18.72p = 93.6p a day, or £341.64 over 365 days, before losses.
- On Intelligent Octopus Go itself, the day rate you would be avoiding is a regional quote (34.95p–38.82p on the fixed version on sale on 15 October 2026), so the gap there is 27.35p–31.22p per kWh, before losses.
- That assumes the house actually uses the full battery during the day, every day. Many homes don’t in summer, or at weekends when they are out.
Round-trip losses
A battery gives back less energy than it takes in. The round-trip efficiency is on the battery’s datasheet. Here is the same 5 kWh a day at four efficiencies, to show how much it matters:
| Round-trip efficiency | Bought at night | Cost at 7.6p | Avoided at 26.32p | Saved per day | Saved per year |
|---|---|---|---|---|---|
| 80% | 6.25 kWh | 47.5p | 131.6p | 84.1p | £306.96 |
| 85% | 5.88 kWh | 44.7p | 131.6p | 86.9p | £317.16 |
| 90% | 5.56 kWh | 42.2p | 131.6p | 89.4p | £326.23 |
| 95% | 5.26 kWh | 40.0p | 131.6p | 91.6p | £334.34 |
These efficiencies are a sensitivity range for the arithmetic, not figures for any product.
The payback question
Payback in years = installed price ÷ yearly saving.
Use the installed price from your own written quotes and the yearly saving from the table above at your battery’s datasheet efficiency, with your own day rate in place of 26.32p. This page doesn’t give a payback figure because it would need an installed price, and I don’t have a sourced one to use.
- Degradation and warranty. Usable capacity falls with age and cycles. Read the warranty for the guaranteed capacity at the end of the term, and any cycle or energy-throughput limit; a daily cycle uses that allowance up faster.
- Tariff rules. Check your tariff’s terms on charging a home battery in the cheap hours, and whether a battery affects eligibility. Octopus, for example, publishes separate advice on choosing between Intelligent Octopus Go and its Flux tariff for battery owners.
- Installation. A fixed home battery is an electrical installation. Get several written quotes from certified installers.
The small version: a portable power station
The same maths works at a smaller scale. The EcoFlow RIVER 2 Pro listed on the best off-peak products page is 768 Wh, so filling it from empty costs 5.8p at 7.6p, against 20.2p at 26.32p, before losses. Used once a day, that is at most £52.48 a year: useful for running a laptop or router in the day, not a whole house.
EcoFlow RIVER 2 Pro on Amazon (paid link)
If you have, or are planning, solar panels as well, the trade-offs are different: export payments and summer charging come in. The tariffs with a cheap window are in UK EV tariffs compared, and the standing charge, which a battery doesn’t change, is explained in standing charge explained.
Questions people ask
Is a home battery worth it without solar?
It can save money on a cheap night rate: about 18.72p per kWh moved from 26.32p to 7.6p, before losses, or 93.6p a day for a 5 kWh battery used fully every day. Whether that is worth it depends on the installed price in your quote: payback = price ÷ yearly saving.
How much does a home battery save on Intelligent Octopus Go?
The saving per kWh is your day rate minus 7.6p, less round-trip losses. On the fixed version on sale on 15 October 2026, the day rate is 34.95p–38.82p depending on region.
Does a battery reduce the standing charge?
No. It only changes when you buy kWh. The standing charge is the same.
Is this financial advice?
No. It is arithmetic for planning. Get written quotes and read the warranty and tariff terms before you buy.
Not financial advice. These are worked examples from published rates and EV-Database consumption estimates, for planning only. Your own tariff, day rate, standing charge, car, driving and weather will change the numbers. Check your bill and your supplier’s current terms before you switch or buy anything.
Sources
- Octopus Energy, Intelligent Octopus Go (checked 15 October 2026)
- Octopus Energy tariff API, Intelligent Octopus Go 12M Fixed October 2026 v1 (regional day rates)
- Octopus Energy, EV tariffs FAQ (Intelligent Octopus Go or Flux for solar and battery owners)
- Ofgem, energy price cap unit rates and standing charges (1 October–31 December 2026)
- SmartShift UK, best off-peak products (EcoFlow RIVER 2 Pro, 768 Wh)
- SmartShift UK, UK EV tariffs compared (checked 15 October 2026)
This page has one Amazon link, marked “paid link”, which uses the tag smartshiftuk-21. If you buy through it, SmartShift UK may earn a commission at no extra cost to you. It doesn’t change the numbers here.