A good lithium home battery comes with a ten-year warranty. It does not stop on the day the warranty ends. How long yours lasts depends on how many cycles it makes, how deep it discharges and how warm or cold it stands. The warranty tells you what the maker promises, but only under its conditions. For a large home with back-up, plan the system for its tenth year, not its first.
You have a quote for a large battery, and the numbers raise one question. One Belgian home owner put it bluntly on Reddit. "The earliest possible for me to earn my money back was 13 years, warranty on the battery's was 10." Another owner saw his system fall back on the grid at 28%, then at 40%. His installer said everything was fine.
The hidden cost is not only money. In a premium home, the battery is also your back-up. A battery that has lost a quarter of its capacity keeps the house running for fewer hours in a power cut. And a warranty with a condition you never read can be void when you finally need it.
That is why we state the warranty in every project. In Wingene, our semi-off-grid system with 150.4 kWh of storage came with a 10-year warranty. In a three-phase house on our solutions page, the lithium batteries carry a 10-year warranty on 80% of their capacity.
How long does a home battery last, in years and in cycles?
A lithium home battery ages on two clocks at once: the calendar and the number of cycles it makes. The EU Battery Regulation therefore obliges the maker to state the expected lifetime in both cycles and calendar years.
A cycle is one full charge and discharge. Two half discharges count as one full equivalent cycle. A battery that fills with solar power by day and empties at night makes about one cycle a day. That is roughly 365 cycles a year, or 3,650 in ten years.
The lifetime a maker states is measured under reference conditions: a set charge and discharge rate, a set depth of discharge and a set temperature. Since 18 August 2024, a rechargeable battery above 2 kWh must come with a document that lists its expected lifetime and those test conditions. A home battery falls under that rule, because the regulation treats every stationary storage system as an industrial battery.
Tip
Compare cycle figures only when the test conditions match. A cycle life measured at a gentle rate and a shallow depth says little about a battery that feeds a heat pump and a car.
What is degradation, and how do you notice it in a large home?
Degradation means that the battery slowly stores less energy and delivers less power than when it was new. The regulation names three signs: capacity fade, power fade and a rise in internal resistance.
| Sign | What happens | What you notice at home |
|---|---|---|
| Capacity fade | The battery holds fewer kWh than its rated capacity | The battery is empty earlier in the evening; back-up lasts fewer hours |
| Power fade | The battery can deliver less power at the same voltage | Heavy loads such as a heat pump start or an induction hob push it to its limit sooner |
| Higher internal resistance | More energy is lost as heat, and the voltage drops further under load | The system reaches its low-voltage limit earlier and switches to the grid at a higher charge level |
Source: Regulation (EU) 2023/1542, annex IV. The last row explains the owner who fell back on the grid at 40%. A battery can still hold its energy, but the voltage sags under load and hits the limit first. Whether that is ageing or a setting that needs recalibrating is something only the data can show.
Usable energy left for the evening and for back-up, example of a 30.8 kWh home battery
A battery at 80% is not worn out. It simply does less of the same work. In a large home with a heat pump and back-up circuits, you notice those missing kWh in a power cut.
What wears a home battery out faster?
Deep discharges, extreme temperatures, high currents and many cycles wear a battery out faster. The EU Battery Regulation lists most of these as the data a battery management system must track.
- Deep discharges. The battery management system must count them. A minimum charge level set too low makes them more frequent.
- Heat and cold. The regulation tracks time spent in extreme temperatures, and time spent charging in extreme temperatures. One maker excludes damage from temperatures above 50 °C or below -10 °C from its warranty.
- High charge and discharge rates. Cycle life is always measured at a stated rate. A small battery that feeds a heat pump and a car charger works at a higher rate than a large one.
- Many cycles. Charging the car from the battery or trading on quarter-hour prices adds cycles and energy throughput.
- Long periods without use. The same maker excludes deterioration caused by six months or more without operation.
Sources: Regulation (EU) 2023/1542, annexes IV and VII; BYD Battery-Box Premium HVS & HVM Limited Warranty Europe, clause 2.3.
Where the battery stands matters as much as how you use it. A technical room that stays frost-free in winter and cool in summer protects the cells better than an unheated garage or an attic.
What does a home battery warranty actually cover?
A home battery warranty usually has two parts: a product warranty against defects and a performance warranty on the capacity that remains. The performance part often ends on a time limit or an energy limit, whichever comes first.
Take the European warranty of one widely used high-voltage home battery, the BYD Battery-Box Premium HVS and HVM. It is a good example of how these documents are built:
| Part of the warranty | What this example says | What to check in yours |
|---|---|---|
| Product warranty | 10 years free of defects in materials or workmanship | Who gives it: the maker, the installer or both |
| Performance warranty | 60% of usable energy after 10 years, or the minimum energy throughput, whichever comes first | The percentage (60%, 70% or 80%) and the energy limit in MWh |
| Start date | Six months after the production date, or 30 days after delivery to the site if you can prove it | Whether the clock starts at production, delivery or commissioning |
| Extra modules | The performance warranty of a module added later runs from its own sale date | How an expansion is covered |
| Remedy | Repair, replacement or a partial refund, at the maker's choice | Whether labour and transport are included |
Source: BYD Battery-Box Premium HVS & HVM Limited Warranty Europe, clauses 1.1 to 1.4 and 3. The energy limit is the clause most owners miss. For the 10.24 kWh model, it is 30.82 MWh: about 3,010 full cycles.
When the energy limit ends the performance warranty (example: 10.24 kWh battery, 30.82 MWh limit, 10-year term)
Then there is the law. In the EU, the seller is liable for any defect that existed at delivery and appears within two years. That legal guarantee covers a faulty battery, not the normal loss of capacity over the years. The maker's commercial warranty covers that ageing, and it binds the maker under the conditions in its warranty statement.
Which conditions can void a home battery warranty?
Most warranties exclude damage caused by installation errors, the wrong inverter, extreme temperatures and repairs without approval. Some also ask for access to the battery data and a quick report of the fault.
The same European warranty lists, among others, these conditions:
- Installed and operated according to the manual, and installed within one month of the warranty start date.
- Only with a certified inverter from the maker's compatibility list.
- No temperatures above 50 °C or below -10 °C, and no shaking or moving after installation.
- Report the fault within 30 days of noticing it.
- No modification or repair without approval of the maker or its service partner.
- Give access to the performance data over the internet when you file a claim, and keep the invoice and serial numbers.
Source: BYD Battery-Box Premium HVS & HVM Limited Warranty Europe, clauses 2.3, 2.4 and 4.
Important
Adding a battery to an existing solar installation? Check that the battery and the inverter are on each other's compatibility list before you buy. Our article on adding a battery to an existing SMA or SolarEdge installation explains the options.
How do you know the state of health of your home battery?
Since 18 August 2024, the battery management system of a stationary storage system must hold up-to-date data on its state of health and expected lifetime. The person who legally bought the battery is entitled to read-only access.
State of health
- Remaining capacity
- where possible remaining power, round-trip efficiency and internal resistance
- how self-discharge evolves
Expected lifetime
- Date of manufacture and of putting into service
- energy and capacity throughput
- full equivalent cycles
- deep discharges and time at extreme temperatures
Source: Regulation (EU) 2023/1542, article 14 and annex VII. The law names the purposes: judging the residual value and remaining life, offering the battery to an aggregator, and preparing it for reuse.
From 18 February 2027, a new battery above 2 kWh also gets a battery passport behind a QR code. Its public part includes the expected lifetime in cycles and the period of the commercial warranty for the calendar life. How the passport works is explained in our article on the EU Battery Regulation.
Tip
Ask before you sign how you will read the health data: in an app, on a web portal or through your installer. With our systems you follow production, consumption and the battery in the free VRM app and portal.
Why should a premium home battery be sized for its tenth year?
A large home asks the most from its battery when ageing hurts most: winter evenings, heat pump starts and long power cuts.
Three choices keep a system useful as it ages:
- Size with a margin. Work out the kWh your house needs for a winter evening or a power cut. A battery at 80% must still deliver them.
- Size the power per phase, not only the storage. Power fade hits heavy loads first. In a three-phase house, that is a choice per phase, as our article on three-phase home batteries with full back-up explains.
- Choose a modular battery. A modular system can be expanded later. Check how the warranty covers modules added later, and whether old and new modules can work together.
Our verdict
A premium home battery does not fail on a fixed date. It slowly does less. Size it so that its tenth year still covers the evening and your back-up, and you will rarely notice the difference.
What happens when a home battery drops below its warranty level?
First, measure: a battery that seems weaker is not always worn out. A wrong setting or a calibration issue can look like ageing, as the owner who fell back on the grid at 40% found out.
When a home battery seems to weaken
We connect new batteries and also revise batteries that are already installed. We also carry out maintenance and repair work on battery systems that are already installed. In Lokeren, the owner's solar panels and inverters stayed in place and were combined with a new 16 kWh battery.
At the real end of its life, a lithium home battery goes to recycling. In our Battery Disassembly Center we take apart lithium batteries from cars, bicycles and home batteries.
What should you ask about lifetime and warranty before you buy?
Ask for the lifetime and warranty in writing, with the conditions, before you compare prices. These questions separate a premium system from a cheap one.
Which lifetime in cycles and years, under which test conditions?
Charge and discharge rate, depth of discharge and temperature, as the regulation requires.
Which capacity is warranted, and until when?
The percentage after how many years, and the energy limit in MWh.
Who gives the warranty?
The maker, the installer or both, and who handles a claim.
When does the warranty start?
Production date, delivery or commissioning.
Which conditions void it?
Inverter list, temperatures, data access, reporting deadlines, months without use.
How do I read the state of health?
App, portal or installer, and whether a third party can read it for you.
How does the system react as it ages?
Back-up hours and power per phase at 80% capacity, and whether modules can be added.
Want a home battery sized for its tenth year, with back-up? Talk to one of our battery specialists.
How do we build a home battery that lasts?
We measure first, design for your use and connect your important systems to the battery. Our team includes three certified battery experts.
- Step 1: We measure your consumption and your peaks before we design anything.
- Step 2: We choose the battery, the inverter-chargers and the back-up circuits for your home. We connect almost all inverter types to the home battery.
- Step 3: We install and commission the system. In a power cut, the inverter takes over within 20 milliseconds.
- Step 4: You follow the system in the free VRM app and portal, and we stay available for maintenance, revision and repair. Our home batteries with back-up come with a 10-year warranty on retained power. See our three-phase projects in Wetteren and Kortenberg.
Frequently asked questions
Does a home battery stop working when the warranty ends?
No. The warranty ends, the battery does not. It keeps working with the capacity it has left, which keeps falling slowly. Check its state of health to know how much that is.
How many times can a home battery be charged?
The answer is in the document with the expected lifetime in cycles, together with the test conditions. In the warranty example above, the energy limit equals about 3,010 full cycles. Two half charges count as one full cycle.
Does charging the electric car from the home battery shorten its life?
It adds cycles and energy throughput, so it uses up an energy-limited warranty faster. It also asks for more power. Whether it makes sense depends on the size of the battery and how often you do it.
Does a home battery need maintenance?
It needs a regular look more than a toolbox: firmware, the minimum charge level, alarms and the state of health. We carry out maintenance and repair work on installed battery systems.
What is the legal guarantee on a home battery?
In the EU, the seller is liable for defects that existed at delivery and appear within two years. Normal ageing is covered by the maker's commercial warranty, under its own conditions.
Can I keep an older battery on back-up when it has lost capacity?
Yes, as long as it still delivers the power your back-up circuits need. Check the back-up hours at its current capacity. Our article on home batteries with back-up explains how to choose the circuits. Want to go further, without the grid? Read which home battery really works off-grid.
Want a home battery that still does the job in ten years?
Tell us about your home, your heat pump, your car and what must keep running in a power cut. One of our battery specialists will size a system for its whole life and show you its warranty in writing.
Sources
- EUR-Lex: Regulation (EU) 2023/1542 on batteries and waste batteries (articles 3, 10, 14 and 77; annexes IV, VII and XIII)
- EUR-Lex: Directive (EU) 2019/771 on contracts for the sale of goods (articles 10, 11 and 17)
- BYD Battery-Box downloads: Battery-Box Premium HVS & HVM Limited Warranty Europe, V1.2