Home Battery Warranties: Retained Capacity, Throughput and Conditions

A home battery is one of the most expensive single items a household buys on the road to energy independence, and the warranty is the document that decides what happens if it does not perform. Most warranties in the UK market run for ten years and carry a retained-capacity promise: the maker guarantees the battery will still store a stated share of its original energy at the end of the period, commonly around 70% after ten years¹. But the small print matters as much as the headline. Warranties can also end early when a throughput or cycle limit is reached, and they can be voided outright by missed registration, a lost internet connection, an unqualified move of the unit or a DIY installation².

This page explains the three ways a battery warranty is written, by years, by energy throughput and by retained capacity, and the conditions attached to each. It covers when the clock starts, what happens on a house sale, how a claim is made, and what the warranty does and does not promise about backup power in a cut.

Warranty scope explained: the product and how it performs

A home battery warranty is really two promises in one document. The first is a product warranty: if the unit fails because of a manufacturing defect, the maker repairs or replaces it. The second is a performance warranty: the maker guarantees the battery will retain a share of its original storage capacity over a set number of years. The performance promise is the one that matters most over a decade of use, because all batteries degrade with every charge and discharge cycle, and the warranty sets the floor under how far that degradation can go before the maker owes you something².

What is covered is not unlimited. SolaX, for example, states that its residential battery warranty "does not include any accessories and tool kit items provided with the product"². The battery cells and enclosure are covered; the small items shipped in the box are not. Which? notes that battery systems often come with a 10-year warranty, but that figure is a market norm rather than a rule, and the terms behind it vary by maker¹.

The distinction between product and performance cover also shapes what a claim looks like. A failed component is a straightforward defect claim. A battery that still works but stores noticeably less than the guaranteed share is a performance claim, and it depends on the maker's own testing of the unit against its nameplate rating⁴. Both routes are subject to the conditions in the document, which is why the rest of this page works through them in order.

How long cover lasts: ten years standard, fifteen at most

Ten years is the standard term for a home battery warranty in the UK. Which? reports that battery systems often come with a 10-year warranty¹, and the independent guidance on lifespan lines up with it: Energy Saving Trust puts the typical lifespan of a battery at about 10 to 12 years⁵, while Home Energy Scotland gives a wider 10 to 15 years⁶. The two figures differ, and both are estimates of typical life rather than guarantees, but they bracket the same territory: a battery bought today is expected to be working into the mid-2030s.

Some makers go beyond the norm. Enphase covers its IQ Battery 5P with FlexPhase for 15 years or 6,000 discharged cycles, whichever is earlier⁴. At the other end of the market, the Plug-In Car Grant criteria required a minimum five-year warranty on the battery and drivetrain for eligible vehicles, which shows how much shorter battery warranties were when the technology was newer⁸. Electric vehicle makers now commonly offer battery warranties of at least eight years or 100,000 miles⁹, with independent guides putting the typical figure at seven or eight years¹⁰ or around eight years or around 100,000 miles¹¹. Home battery warranties are, on the whole, longer than EV battery warranties, because a home battery typically cycles once a day rather than being driven and fast-charged.

The headline years figure is only half the story, though. A warranty that runs to year ten or fifteen can still end in year six if a throughput or cycle limit is reached first, which is the subject of the throughput section below. When comparing warranties, read the years figure and the energy limit together, not separately.

Capacity retention: the benchmark of 70% over ten years

The retained-capacity clause is the heart of a battery warranty. It promises that after a stated number of years, the battery will still hold a stated share of the energy it held when new. SolaX's guidance describes the industry range as 60 to 80% of original nominal energy, and states that "most manufacturers guarantee around 70% capacity after 10 years"². That 70% after 10 years figure is the benchmark to expect, and a warranty that promises materially less deserves scrutiny.

Individual makers set their own numbers. Enphase guarantees that a covered IQ Battery will "maintain the ability to store and discharge an energy capacity of at least (i) 70% of the Covered IQ Battery nameplate rating" at the end of the tenth year of the warranty period⁴. BYD's Battery-Box Premium warranty promises the product will "retain sixty per cent (60%) of its Usable Energy for ten (10) years from the Warranty Start Date; or (ii) reach the Minimum Throughput Energy, whichever comes first"⁷. BYD's 60% is lower than the common 70%, but it is paired with a throughput allowance that can end the cover on a different schedule.

The end-of-life capacity threshold a maker chooses, 60%, 70% or 80%, feeds directly into how the battery serves the house in its later years³. A battery guaranteed to 80% has further to fall before the maker owes a remedy, but it also promises more usable storage in year nine. A household sizing a battery for self-sufficiency should read the retained-capacity figure alongside the usable capacity on the specification sheet, because the warranty tells you what the battery is guaranteed to deliver at the end, not just on day one.

Cycle and throughput caps that may cut cover short

Throughput is the second way warranties are written, and the one most often missed. Battery throughput, or energy throughput, is "the total amount of energy a battery can charge and discharge over its entire lifetime, usually measured in kWh or MWh"³. A warranty with a throughput limit ends when that total is reached, regardless of how many years remain. SolaX's guidance is blunt about the consequence: "many battery warranties end when the system reaches its throughput limit, even if the time period hasn't expired"³, and its warranty guide adds that "the warranty usually ends when either the cycle limit or the time limit is reached, whichever comes first"².

The practical effect depends on how hard the battery is worked. A household that cycles the battery fully once a day, charging on a cheap overnight rate and discharging through the evening, burns through a throughput allowance faster than a household that only cycles it on sunny days with solar. This is where the warranty interacts with how the battery is used: aggressive tariff stacking or grid-service participation increases throughput and can shorten the warranty's effective life.

myenergi's libbi warranty carries one of the most specific clauses of this kind. It states: "If you choose to connect to a third party system or manually operate the Battery pack outside of our Controller, the warranty expires when a maximum of 3MWh/per kWh usable capacity has been reached"¹². That is an allowance of 3 MWh for every kWh of usable capacity, and it applies only when the battery is run outside myenergi's own controller. Staying within the maker's ecosystem keeps the fuller warranty in place.

To work out how long an allowance lasts, divide the total by the energy cycled each year: a throughput cap bites sooner in a household that charges and discharges the battery every day than in one that uses it only for occasional backup. The same arithmetic applies to cycle limits, which count completed charge and discharge cycles rather than the energy moved. Whichever limit arrives first, the time term or the throughput or cycle cap, is the boundary of the maker's promise. Neither figure is a prediction of a battery's life, only the edge of the cover.

Circumstances that invalidate your cover

The conditions section of a warranty is where cover is won or lost, and battery warranties carry more of them than most household products.

• Registration deadlines. SolaX states that "if the system was not registered within 90 days, the warranty automatically starts 6 months after the battery left the factory"², which silently shortens the cover. Boiler warranties show the same pattern, with registration required within 30 days of installation¹³.
• Connectivity. Enphase requires that "the Covered Products must be continuously connected to the internet during the Limited Warranty Period, except where interrupted by causes outside of the Covered Owner's reasonable control"⁴. A router change or a switched-off hub can put cover at risk.
• Moving the unit. SolaX warns that "moving the battery after its first installation, even to the same address, voids the warranty unless a qualified installer" re-tests it².
• Unauthorised repairs and parts. SolaX: "Do not replace the battery or accessories without prior consent from SolaX, as this can void the claim."²
• DIY installation. Attempting a DIY installation with high-voltage DC runs "will instantly void your product warranties"¹⁴.
• Siting and temperature. Installing a battery in uninsulated areas that experience ambient temperature extremes can void coverage¹⁴, which links to the wider rules on where a battery can be installed.
• Third-party additions. Connecting a wind turbine to an existing battery using a bespoke arrangement "carries the expensive risk of invalidating warranties for the battery, inverter and possibly the wind turbine too"¹⁵.

When cover begins: registration and the activation countdown

When a warranty starts is not always when the battery is fitted. SolaX's residential battery warranty "begins from the earlier of the installation date or 6 months after the production date"². That means a battery that sat in a distributor's warehouse for months may already have lost warranty time before it reached the wall. BYD's warranty start date is "the first day after six (6) months from the Production Date of the Product, or at the Original Buyer's choice the first day after thirty (30) days from the Delivery Date if proven in writing"⁷. Enphase defines the Activation Date as "the earlier of (i) the date the Covered Product is registered with Enphase, or (ii) the date the Covered Product is activated at the Original Location via the Enphase's Installer Portal"⁴.

The common thread is that the clock can start without you. Production-based start dates protect the maker against stock sitting unsold, and registration-based systems shift the burden onto the household and installer to complete the paperwork promptly. Enphase adds a hard physical deadline: its warranty "does not cover IQ Batteries that are activated after the 'Energize by' date indicated on the IQ Battery or packaging"⁴, so a battery bought cheaply as old stock may have no warranty at all if activated too late.

For the household, the practical steps follow from the rules. Confirm at handover that the installer has registered the system with the maker, note the registration date, and keep the proof of purchase and serial numbers, which myenergi requires for a claim¹². The installer's role matters here too: an MCS-certified installation with proper handover documentation is what makes the registration deadlines achievable.

Enphase IQ Battery 5P: fifteen years, but tight time limits

Enphase's UK storage warranty, effective for products activated on or after 15 September 2025, is one of the longer terms on the market and one of the stricter documents. The IQ Battery 5P with FlexPhase is covered for the earlier of 15 years from the Activation Date or 6,000 discharged cycles⁴, and the product page confirms the 15-year warranty up to 6,000 cycles¹⁶. The battery is an all-in-one, AC-coupled unit with 5.0 kWh of usable capacity, usable on single-phase and three-phase installations¹⁶.

The warranty's territorial extent is "Scotland, England, and Wales"⁴, so Northern Ireland households should check what terms apply to them before buying. The retained-capacity promise is at least 70% of the nameplate rating at the end of the tenth year⁴. Other components carry shorter terms: the IQ System Controller is covered for 10 years from the Activation Date, while the System Shutdown Switch, IQ Gateway, Mobile Connect, Consumption CT and Communications Kit are covered for 5 years⁴.

The strict parts are in the conditions. Beyond the continuous internet connection requirement, the warranty applies solely to product imported into the European Economic Area, Switzerland or the UK with Enphase's consent, and product imported without consent may be refused activation⁴. On a claim, if the defective product is not received by Enphase within sixty days of Enphase providing an RMA number, the claim fails⁴. After a repair or replacement, the warranty continues for the remainder of the original period or ninety days from receipt of the repaired product, whichever is later⁴. The document is governed by the laws of England⁴.

Solplanet: inverter cover and extended options

The battery is not the only component with a warranty: the inverter that sits beside or inside it has its own, usually shorter, term. Solplanet offers end-users a standard warranty of up to 5 years on its inverters, and "the warranty can also be extended for up to 10 years"¹⁷. The maker states the standard warranty applies "without affecting the legal warranty provided by any wholesaler or retailer"¹⁷, which matters because the statutory rights against the seller are separate from and unaffected by the maker's own warranty.

Solplanet's claims process is direct: customers contact its customer support department or use an online claim form, and "if necessary, our logistics network will deliver a replacement inverter directly to you"¹⁷. That replacement-delivery promise is worth noting because inverter failures take the whole storage system offline, and the speed of the logistics chain determines how long the household goes without its battery.

Sungrow's UK material emphasises the benefits of its inverter systems, including "reducing waste" of home solar generation¹⁸ and the reassurance of "knowing that your house is guarded from potentially dangerous power outages"¹⁹. Those are marketing claims about the system's purpose rather than warranty terms, and the backup claim in particular should be checked against the product's actual capability, as the next sections explain. For Sungrow's storage warranty terms, see the maker's own documentation.

How warranties sit alongside your legal consumer rights

A manufacturer's warranty sits on top of your statutory rights, not instead of them. Citizens Advice explains that claiming under a warranty or guarantee is one route when something goes wrong with a purchase, and that a claim needs details of what the problem is²⁰. The warranty is a voluntary promise from the maker; your legal rights against the retailer who sold you the system are separate and cannot be taken away by warranty small print.

The time limits on those statutory rights differ across the UK. Enphase's own warranty document states the position plainly: "For goods purchased in England and Wales, these rights expire six years from delivery of the goods." and "For goods purchased in Scotland, these rights expire five years from delivery of the goods."⁴ A household in Edinburgh and a household in Manchester buying the same battery have different statutory windows, even with identical warranties.

Two practical points follow. First, a warranty that has expired, or been voided by a condition, does not necessarily remove your rights against the seller for goods that were not of satisfactory quality. Second, official schemes can carry their own warranty requirements: an approved ECO4 innovation measure specifies "an unreplaceable battery with a twelve-year manufacturer's warranty"²¹, which shows what warranty standard public funding bodies expect when they pay for storage.

Claims process: time limits, RMA references and replacement units

A warranty claim is a process with deadlines at each step, and missing one can end it.

1. Report the fault promptly. BYD requires the buyer to "notify BYD or a BYD Authorized Service Partner of the defect or deterioration within 30 days" of becoming aware of it⁷. Insurance-backed workmanship schemes commonly set a 30-day reporting window too²².
2. Gather the evidence. myenergi requires "proof of purchase of your Product and its serial numbers"¹²; Citizens Advice lists "details of what the problem is" as the core of any claim²⁰.
3. Contact the maker. Enphase lists a UK support line, +44 (0)1908 828928⁴. Solplanet directs claims to its customer support department or online claim form¹⁷.
4. Obtain and act on the RMA number. Enphase issues a return authorisation, and "if the allegedly defective Covered Product is not received by Enphase within sixty (60) days of Enphase providing an RMA" number, the claim fails⁴.
5. Check the replacement's cover. Enphase's warranty continues on a repaired or replacement product for the remainder of the original period or ninety days from receipt, whichever is later⁴.

If the maker or installer does not resolve the matter, escalation routes exist. The Energy Ombudsman's eligibility checklist requires that you complain to the supplier first, wait 8 weeks or receive a Deadlock Letter, have sufficient evidence including the date you raised the complaint, and confirm the supplier name matches the bill²³. The same 8-week rule appears in its heat network guidance: "You need to wait 8 weeks after your first complaint to your supplier."²⁴ Those are not battery warranties, but they show the pattern of short reporting windows across household energy products.

Backup mode and the limits of what is guaranteed

Backup power is where expectations and warranties most often diverge. Not all batteries can deliver electricity during a power cut, the Centre for Sustainable Energy states plainly²⁵, and Electricity North West notes that "in some cases these storage devices can provide back-up supplies for use in a power cut, but this is not always possible"²⁶. Which? advises asking your installer whether the battery will work in an outage, and for how long¹. Backup capability is a function of the system design and changeover arrangement, covered in detail on battery backup and EPS, not a promise the warranty makes.

Enphase's warranty draws a hard line on one use: "Covered Products are not intended for use as a primary or backup power source for life-support systems, other medical equipment, or any other use where product failure could lead to injury, loss of life, or catastrophic property damage."⁴ Any household relying on mains power for medical equipment needs a dedicated solution, not a home battery.

There is also a floor on how far a battery discharges. Energy Saving Trust explains that "when the battery gets down to a set level, maybe 20% of the total storage capacity, your system will stop taking electri"city from it⁵, a reserve that protects the cells but reduces what is available in an outage²⁷. The warranty guarantees the cells against degradation; it does not guarantee the lights stay on.

Passing cover to a new owner

A battery is fixed to the house, so what happens to its warranty when the house changes hands matters to both seller and buyer. The answers differ by maker. myenergi's libbi warranty is "transferrable to a new owner of your property should you sell your house and choose to leave" the product, with customer service contacted to arrange it¹². Enphase takes a more formal route: the transferee must pay the applicable transfer fee set out in the Change of Ownership Form "within thirty (30) days from the date of transfer"⁴. Enphase also charges a restocking fee in some circumstances, equal to the higher of 15% of the original purchase price or the retail value of missing parts⁴.

Workmanship warranties, which cover the installation rather than the product, behave differently again. The OFTEC scheme rules state that "a workmanship warranty is fully transferable between owners of a property" and passes automatically to the new owner if the home is sold, for the duration of the warranty period²⁸. So a buyer may inherit the installer's workmanship cover without doing anything, while the battery maker's cover needs paperwork and possibly a fee.

For a seller, an untransferred warranty is a lost selling point; for a buyer, an untransferred warranty is a battery with no cover. Either way, the transfer should be on the conveyancing checklist alongside the home insurance notification.

The role of a warranty in energy self sufficiency at home

A home battery is bought for independence: the MCS definition of self-sufficiency is "the percentage of electricity consumed in the property over a year which is met by either behind the meter solar or electrical energy storage"²⁹, and Solar Energy UK's framing is that "more homegrown energy means greater energy independence"³⁰. The warranty underwrites that independence for a decade or more. It is the maker's promise that the asset will keep doing the job it was bought for, and the retained-capacity clause tells you exactly how much of the job is guaranteed in year ten.

But the warranty also maps the dependencies that remain. A connectivity condition ties the household's cover to a working internet connection and, in practice, to the maker's cloud and app⁴. A registration condition ties it to paperwork completed on time². A throughput limit ties it to how the battery is used³. And the warranty's survival ties it to the manufacturer's own existence as a company: a promise from a maker is only as durable as the maker. None of this removes the independence the battery delivers day to day, but it is the fine print that decides whether that independence is protected when something goes wrong.

Reading the warranty before buying is therefore part of the purchase decision, not an afterthought. Compare the years, the throughput allowance and the retained-capacity percentage together; check the start-date rule, the registration deadline and the connectivity condition; and confirm what happens on a house sale. The Energy Switch Guarantee works on the same principle in a different market: a list of 10 commitments that protect households through a process³¹. A battery warranty is the equivalent list of commitments for the most expensive component of a self-sufficient home, and it deserves the same scrutiny before signing.