Home Battery Warranties and Cycle Counts Explained
- Warranties usually set limits in years and in cycles or total energy throughput.
- A cycle is a discharge equal to the usable capacity, and partial discharges add up.
- Look for a stated minimum capacity at the end of the warranty.
- Conditions such as installer, temperature and connectivity can affect cover.
- Check who pays if the installer stops trading.
A home battery warranty usually promises a number of years, a limit on use and a minimum remaining capacity at the end. The small print on cycles, conditions and who honours a claim matters as much as the headline years.
Years, cycles and throughput
Three limits recur in warranties: years from installation, a cycle count, and total energy throughput, usually in MWh. Whichever limit is reached first normally ends the cover. Some manufacturers use cycles, some use throughput, and some use both.
One full cycle is a discharge equal to the battery's usable capacity, and partial discharges add up. As an example, a battery with 10 kWh usable that delivers 8 kWh a day completes 0.8 of a cycle a day. That is about 292 cycles a year, or roughly 2,900 over ten years. Check how your manufacturer counts, because a throughput limit and a cycle limit can behave differently.
Retained capacity
A battery loses capacity with use. Warranties normally state the minimum capacity it should still have at the end, as a percentage of the original. Ask for that figure and how it is measured, including the test conditions. A long term with no retained-capacity figure tells you very little.
This links to efficiency and sizing. If a battery will have lost some capacity by the end of its life, check that the size you buy still covers your needs then. Our battery capacity guide can help you judge that.
Conditions and exclusions
Cover often depends on how the battery is installed and used. Check whether the warranty requires or limits any of the following:
- installation by an approved or certified installer
- registration within a set period after installation
- operating temperature, ventilation and location
- an internet connection and firmware updates
- use for grid services or trading, which adds cycles
- transfer to a new owner if you sell the property
Get it in writing
Ask the installer for the full warranty document before you sign, and keep it with your commissioning paperwork.
What is covered and who pays
Ask what is covered: the battery modules, the inverter, labour, and removal and reinstallation. Then ask who honours the warranty, the manufacturer, the installer, or an insurance-backed guarantee. If the installer stops trading, find out whether the manufacturer's cover continues and whether a third-party guarantee is available.
Headline terms can look generous. Octopus Energy said on 22 June that its Nook battery range would carry a 12-year warranty, as set out in its announcement. We could not find the cycle, throughput or retained-capacity terms behind it. A long headline term is a good start, but it is not an answer on its own.
Common questions
Is a longer warranty always better?
Not by itself. A 15-year term with tight cycle limits can be worth less to you than a 10-year term with generous limits. Compare years, cycles or throughput, and retained capacity together.
What counts as a cycle if I only use half the battery?
Two half discharges add up to roughly one cycle. Partial use does not reset the count, so your daily pattern determines how fast you use up a cycle limit.
Does using a battery on a dynamic tariff use up the warranty faster?
It can, if you cycle more often. Estimate your likely cycles per year and check them against any limit in the terms. See how to earn money with a battery on a dynamic tariff for how often tariffs call for cycling.
Can I transfer the warranty if I sell my home?
It varies by manufacturer. Ask in writing whether it transfers and whether the new owner has to register.
Related guides
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