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BatteriesBattery warranties and what retained capacity really means
A battery warranty is three promises in one document: how long it lasts, how much capacity is guaranteed at the end, and how hard you are allowed to work the battery in between. Miss the third one and the first two mean less than you think.
Updated 4 August 2026 · written by the Clearline guidance team
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What a battery warranty actually promises
Every home battery warranty is built from the same three parts. A term, in years. A retained capacity figure, which is the share of the original usable capacity the manufacturer guarantees will still be there when the term ends. And a usage limit, expressed either as a number of charge and discharge cycles or as a total energy throughput in kWh. Cover ends when the first of those is reached, not the last.
Whichever comes first
A 15 year warranty capped at 6,000 cycles is not a 15 year warranty if you cycle the battery harder than the manufacturer assumed. Read the term and the usage limit as a pair, because the document pays out on whichever runs out first.
- Warranty
- 10 years, 80 per cent capacity retained at 10 years
- Usable energy
- 13.5 kWh
Retained capacity, in plain terms
Lithium cells hold less energy as they age. Retained capacity is the floor the manufacturer commits to. Tesla warrants the Powerwall 3 in the UK at 80% of original usable capacity after 10 years, so a battery sold as 13.5 kWh usable must still deliver at least 10.8 kWh at the end of the term. Fall below that and the manufacturer repairs, replaces or compensates under the terms of the document.
It is a floor, not a forecast
An 80% guarantee does not mean the battery will be at 80% in year ten. It means the manufacturer is on the hook if it drops below that. Real degradation depends on how deeply and how often you cycle, and on temperature. Treat the number as the worst case you have bought protection against.
Cycles and throughput are two different limits
A cycle is one full charge and discharge, or the equivalent made up of partial ones. At one full cycle a day, 6,000 cycles is over sixteen years of use, which is why the years usually run out before the cycles do on a solar led system. Enphase warrants the IQ Battery 5P for 15 years or 6,000 cycles, whichever comes first, and 6,000 spread across 15 years works out at 400 a year, a shade over one full cycle a day on average.
Throughput limits work differently. Instead of counting cycles, the manufacturer caps the total energy the battery is allowed to move across its life. That clause matters if you plan to trade the price gap rather than just store solar. Charging at an 8p off peak rate and displacing electricity capped at 26.11p per kWh is worth doing every night of the year, including winter, and a battery worked that hard can pass one cycle a day. Tesla's terms allow unlimited cycles for self consumption, time of use and backup use, which is a materially different position from a fixed cycle count. Our guide to off peak arbitrage covers the economics of that pattern.
What the main UK battery warranties say
| Battery | Warranty term | Usage limit | What else is in the document |
|---|---|---|---|
| Tesla Powerwall 3 | 10 years | Unlimited cycles for self consumption, time of use and backup use | 80% of original usable capacity guaranteed in the UK. Requires a reliable internet connection for firmware updates. The 70% figure quoted in some roundups applies only to Italy, Spain, Malta, Portugal and Slovenia. |
| Enphase IQ Battery 5P | 15 years | 6,000 cycles, whichever comes first | The longest headline term in the mainstream UK market. AC coupled, so it retrofits to solar from another manufacturer. These terms come from a UK retailer resource rather than an Enphase warranty document, so confirm them on the PDF for your model. |
| Fox ESS EQ range | 12 years | No cycle cap published on the manufacturer's UK range page | Applies across the EQ modules, which run to a 90% depth of discharge, so compare on usable capacity not headline capacity. |
| Sigenergy SigenStor | 10 years on the battery and the controller | A stated retained capacity or a minimum energy throughput, whichever comes first | Two Sigenergy warranty documents we could reach on 4 August 2026 give different capacity floors for this product: the SigenStor warranty for the EU states 70% usable energy at 10 years, while the factory limited warranty document states 60% retained at year 10. We cannot tell from those documents alone which one governs a UK purchase made today, so verify the current warranty document for your exact model before you sign, and get the percentage in writing. The optional DC EV charging module carries 3 years. |
| Sunsynk ECCO system | 5 years on the ECCO hybrid inverter as standard | Battery module rated up to 6,000 cycles | A useful reminder that the inverter term and the battery term are separate documents with separate lengths. Check both. |
Manufacturer and retailer sources checked 3 and 4 August 2026. Terms vary by model, market and purchase date, so read the warranty document dated for your own installation rather than a comparison table. Where two manufacturer documents disagree, as they do on Sigenergy retained capacity, the current warranty PDF for your model is the only thing that settles it, and we have shown both published figures rather than pick one. Clearline does not supply, install or represent any of these products. Installations are carried out by an MCS-certified installation team for your area.
The longest headline term is not automatically the best paper. A 15 year warranty with a hard cycle cap can expire earlier in practice than a 10 year one with no cycle limit, if the system is worked hard. Sequence matters too: a 12 year term on a battery you intend to cycle once a day is comfortable, while the same term on a battery running two shallow cycles a day is a different risk.
Book a free remote design call and we will read the warranty terms on any quote you have been given, line by line, before you commit.
Get your free quote →The clauses that catch people out
- Connectivity requirements. Some warranties are conditional on the system staying connected to the internet so firmware updates can be applied. A battery sat behind a dead router for two years is a warranty argument waiting to happen.
- Separate terms for separate boxes. The battery, the inverter or controller, the gateway and any EV charging module can each carry a different length. The shortest one is your real exposure.
- Registration deadlines. Several manufacturers require the installation to be registered within a set window after commissioning. That is usually the installation team's job, so confirm it was done and keep the confirmation.
- Usable versus nominal capacity. Retained capacity is measured against the original usable figure, not the headline nominal one, so establish which number the document is using.
- Depth of discharge conditions. Running a module deeper than the manufacturer recommends can sit outside the warranted operating pattern even when the hardware permits it.
- Labour and call out. A replacement cell module supplied free is not the same as a free installation of it. Check whether the manufacturer covers the visit or whether that falls to your installation team's workmanship guarantee.
A warranty is only as good as the company behind it
GivEnergy was, for several years, the best known domestic battery brand in Britain, and it sold its residential range with a 12 year warranty carrying unlimited cycles and a 70% retention guarantee on systems installed from 11 September 2023. On 9 April 2026 GivEnergy Ltd entered administration and ceased trading, with all 74 staff made redundant and unsecured creditors owed more than £17,000,000. The UK Energy Storage Association issued guidance to owners: the hardware is self contained and keeps charging from solar and powering homes, but no further hardware warranties are being honoured by GivEnergy Ltd, and owners should go to their installation team in the first instance. The lesson is not about one brand. It is that a warranty is a promise from a balance sheet, and a long term from a company that may not outlast it is worth less than a shorter term from one that will.
Three layers of cover, not one
The manufacturer warranty covers the hardware. Your installation team's workmanship guarantee covers the fitting. An insurance backed guarantee steps in to honour that workmanship guarantee if the installation team stops trading. What none of them does is honour a failed manufacturer's product warranty, which is exactly the gap the 2026 insolvency exposed. Our guides to insurance backed guarantees and consumer protection schemes set out who covers what.
How to compare two warranties in five minutes
- Ask for the actual warranty PDF for the exact model on the quote, not a link to a brand page or a comparison site.
- Write down three numbers from each: term in years, retained capacity percentage, and the cycle or throughput cap.
- Check what the retained capacity is measured against, usable capacity or nominal capacity, and convert both quotes to kWh so you are comparing like for like.
- List every separate box in the system and its own term. Battery, inverter, gateway, charging module. The shortest term is the number that matters.
- Read the conditions section for connectivity, registration and operating pattern requirements, then confirm in writing who is responsible for each one.
- Ask how long the manufacturer has traded in the UK and who honours the paper if they stop, then check the installation team's workmanship guarantee and insurance backed guarantee separately.
Warranty terms sit alongside the rest of the specification, and the battery storage guide covers capacity, output and backup in more depth. If you want to see what a system would do on your own usage, every county page in our coverage area carries a local calculator built on the same dispatch model our guidance uses, and the tariffs guide explains the off peak rates that decide how hard a battery gets worked. Anything else, the help centre is the fastest route to a straight answer.
Clearline gives independent guidance and a free remote design call. Installations are carried out by an MCS-certified installation team for your area.
Battery warranty questions, answered
What does retained capacity mean on a battery warranty?
It is the minimum share of the original usable capacity the manufacturer guarantees will still be available when the warranty term ends. Tesla warrants the Powerwall 3 in the UK at 80% after 10 years, so a 13.5 kWh usable battery must still deliver at least 10.8 kWh. If it falls below that inside the term, the manufacturer has to put it right under the terms of the document.
Is a longer warranty always better?
Not on its own. A 15 year term capped at 6,000 cycles can expire before a 10 year term with no cycle limit, if the battery is worked hard. Compare the term, the capacity floor and the usage cap together, and weigh them against how likely the manufacturer is to still be trading when you need to claim.
What is the difference between cycles and throughput?
A cycle counts one full charge and discharge, or the equivalent made up of partial ones. Throughput counts the total kWh the battery is allowed to move across its life. Throughput clauses bite hardest on homes doing daily grid charging for off peak arbitrage, because that pattern moves far more energy than a solar only system.
Do I lose my warranty if the battery goes offline?
It depends on the manufacturer. Some warranties are conditional on the system keeping an internet connection so firmware updates can be applied, which is stated in Tesla's terms for the Powerwall. Others are not. It is worth checking before you decide where the router goes, and worth fixing quickly if the connection drops.
What happens to my warranty if the manufacturer goes bust?
The product warranty is a claim against that company, so if it stops trading the claim usually has nowhere to go. That is what happened when GivEnergy Ltd entered administration on 9 April 2026 and hardware warranties stopped being honoured. The hardware itself carries on working. Your installation team's workmanship guarantee and any insurance backed guarantee are separate from the manufacturer warranty and are unaffected by the manufacturer failing.
Does the inverter have the same warranty as the battery?
Often not. Sunsynk supplies its ECCO hybrid inverters with a 5 year warranty as standard while the battery modules are rated for up to 6,000 cycles, and stacked systems can have a different term again on the gateway or an EV charging module. List every component and its own term, because the shortest one is your real exposure.
Should I pay for an extended warranty?
Sometimes, and the question to ask first is what the extension is worth if the manufacturer is not there to honour it. Weigh the cost against the price of the module it protects, check whether the extension is insured by a third party or simply a longer promise from the same company, and confirm whether it covers labour as well as parts.
See the numbers next: Tesla Powerwall 3, installed, or what a battery costs.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- Tesla Powerwall warranty, EMEA: 10 year term, 80% retained capacity in the UK, unlimited cycles for self consumption, time of use and backup, internet connection requirement tesla.com
- Enphase IQ Battery 5P: 15 year term or 6,000 cycles as reported by a UK retailer resource, checked 4 August 2026 (secondary source, not confirmed against an Enphase warranty document) switchtogether.co.uk
- Fox ESS EQ battery range, UK site: 12 year warranty and 90% depth of discharge across the EQ modules fox-ess.uk
- Sigenergy, SigenStor warranty document for the EU: 10 years on battery and controller, 70% usable energy at 10 years or a minimum throughput whichever comes first, 3 years on the DC EV charging module sigenergy.com
- Sigenergy, factory limited warranty document: 60% retained capacity at year 10. This conflicts with the 70% figure in the EU warranty document above and was unresolved at the date on this page sigenergy.com
- Spirit Energy, SigenStor warranty structure summary used as a cross check (secondary source) spiritenergy.co.uk
- Sunsynk ECCO hybrid inverter range: 5 year inverter warranty as standard sunsynk.org
- Sunsynk 5.32 kWh LFP module rated up to 6,000 cycles powerland.co.uk
- GivEnergy residential batteries sold with a 12 year warranty, unlimited cycles and 70% retention for systems installed from 11 September 2023 ukgei.co.uk
- GivEnergy Ltd administration, 9 April 2026: cessation of trading, 74 redundancies, unsecured creditor position ess-news.com
- UK Energy Storage Association guidance for GivEnergy owners: hardware continues to operate, no further hardware warranties honoured, contact your installer first esa-uk.org
- Insurance backed guarantees: what an IBG covers and when the certificate takes effect hies.org.uk
- Workmanship warranty and deposit protection durations across consumer code member insurers recc.org.uk
- Ofgem price cap 1 July to 30 September 2026: 26.11p per kWh average capped unit rate ofgem.gov.uk
- Intelligent Octopus Go off peak rate from 8p per kWh octopus.energy
Read next
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