Commercial battery warranties: what eight makers publish

A commercial battery’s warranty is usually sold as one number: ten years. We read the published warranty documents for eight manufacturers’ commercial battery products to see what sits behind it. The headline term runs from 2 to 15 years depending on what is covered. Where a maker states the capacity it guarantees at the end, the figure is between 60% and 70%, and two of the eight state none. Six of the eight tie some or all of the cover to a connection or registration with the maker’s cloud platform, and seven of the eight start the clock on a date that can fall before the battery is working.

How we did it

On 14 October 2026 we looked for the warranty document of one commercial or industrial battery product from each of eight manufacturers, and read the text of the documents themselves, not summaries of them. The products run from a 102 kWh cabinet to a container of about 4 MWh. The list is not a ranking and is not a recommendation: it is the eight for which we could find and read the terms. A warranty document applies to the region and the sale it names, so the one that governs your purchase is the one in your contract.

What the documents promise

The conditions behind the headline

What the headline hides

The clock can start before the battery is working. Seven of the eight documents start the warranty on a date that can fall before the battery is working. Five use the earlier of installation or commissioning and a fixed period after manufacture, shipment or delivery: 3 months for Fox ESS, 6 months for Sungrow and Sigenergy, 9 months for SolaX and 12 months for SolarEdge. BYD and Huawei use a fixed period alone: BYD 6 months from production, or 30 days from delivery if the buyer can document the delivery date, and Huawei 90 or 180 days from shipment, or earlier on a service request or, for direct sales, an agreed date in the contract. A battery that waits in a store, or waits for a grid connection, uses up warranty while it waits. The network operator’s timescale is outside your control, which is one more reason to start the G99 application early.

“70%” is not one promise. Makers measure the end-of-term capacity against different bases. SolarEdge uses the “indicated” battery capacity, Sungrow the nominal energy output, BYD, Fox ESS and Sigenergy usable energy, and SolaX nominal energy. A guarantee of 70% of nominal energy and a guarantee of 70% of usable energy are different amounts of battery, because usable energy is lower than nominal. Ask for both figures in kWh.

A cycle cap can end the cover before the years do. Five of the eight documents end the performance cover at the first of a number of years, a number of cycles or an energy throughput. At one full cycle a day, 6,000 cycles last about 16 years, so the years end first. At two cycles a day, which a business might run to cover two peak windows, 6,000 cycles last about 8 years and Sigenergy’s 4,200 cycles for higher-rate use about 5.75 years (our arithmetic, from the figures above). Fox ESS states that its policy assumes 2 cycles a day. Work out how often you expect to cycle the battery before you read the years.

The cover can depend on a cloud connection. Six of the eight tie some or all of the cover to a connection or registration: SolarEdge, Sungrow, Sigenergy, Fox ESS, SolaX and Huawei. SolarEdge says plainly that it will not be able to honour the warranty if the product is not connected to its portal, other than for temporary disconnection. Ask what happens if the site’s network is down for a week, who pays for the connection, and what the warranty says if the maker’s platform changes.

Temperature can change the term. BYD’s performance cover is 10 years if the ambient temperature recorded by the unit is 0 to 20 °C, 7 years at 20 to 30 °C and 5 years at 30 to 45 °C. A plant room or an outdoor enclosure in a UK summer can sit above 20 °C, so ask which temperature band the quoted term assumes.

Parts are covered for less time than the battery. Fox ESS covers liquid cooling and the energy management system for 3 years, SolarEdge covers its fans, HVAC and fire suppression for 5 years, and SolaX covers its cooling systems and energy management system for 2. A battery that has kept its capacity can still be out of service because a cooling unit has failed after the cover for it ended.

Few documents name the UK. Sungrow’s is issued by Sungrow Power UK Ltd, and Fox ESS lists the United Kingdom among its countries. Huawei, BYD and Sigenergy name Europe, SolaX defers to the commercial contract, SolarEdge ties its cover to the territory where it originally sold the product and Tesla’s datasheet states no region. Ask which legal entity gives the warranty and whether it covers an installation in the UK.

Terms change between editions. Sigenergy’s January 2025 edition guaranteed 70% with 5,000 and 3,500 cycles, and its May 2026 edition guarantees 60% with 6,000 and 4,200. SolaX’s two copies differ on throughput, and the later one adds the maintenance condition. Ask for the edition date, and for the version to be attached to the contract.

Some terms are not published at all. Tesla’s datasheet gives a term and no retention or throughput figure, and Huawei’s current policy gives none for its air-cooled 200 kWh series. A term you cannot read before you sign is a risk you cannot price.

Questions to put in writing

• Which document governs this purchase, which edition and which legal entity gives the warranty?
• What capacity is guaranteed at the end, in kWh, and against nominal or usable energy?
• When does the warranty start, and does time spent in storage or waiting for a connection count?
• What cycle, throughput or temperature limits apply, and what do they mean at the number of cycles a day we expect?
• Does any cover depend on a cloud connection or registration, and what if the connection fails?
• What must we do to keep it valid: maintenance, certified installers, notice periods?
• Which parts have shorter terms, and what does a failure of one of them do to the battery’s availability?
• Is the UK covered, and who services a claim here?

For the wider decision, our buying guide to commercial battery storage sets out six checks, the UK rules and the steps from first look to a working system, and our quote checklist lists what a quote should state.

Limits of this comparison

It covers eight documents on one day. Some were copies hosted by distributors, not by the maker, and a distributor’s copy may not be the current edition. We did not read every document a maker publishes: Huawei also has older European terms that we did not compare. Terms for a product sold into the UK may sit in a separate document that we did not find. We have not assessed how any maker handles claims in practice, nor its financial strength, and a warranty is only as good as the company that stands behind it. This is not legal advice, and the contract you sign is what binds the maker.

Sources

• SolarEdge, CSS-OU-20 battery cabinet datasheet, DS-000233-ENG, 2 May 2024 and Limited Product Warranty for the Commercial Storage System CSS-OD, undated, file created June 2024 (distributor-hosted copies)
• Sungrow, Supplier’s Warranty for C&I ESS, V2026-04-23, Schedule F (distributor-hosted copy) and ST255CS-2H datasheet
• BYD, Battery-Box Premium LVL Limited Warranty, Commercial, EU, V1.1
• Sigenergy, Factory Limited Warranty for C&I Product, Europe edition of 28 May 2026 and version 1.1 of 20 January 2025 (distributor-hosted copies)
• Fox ESS, C&I ESS Warranty Policy for G-Max Systems, v4.0, 28 July 2026
• SolaX, Warranty Terms and Conditions of ESS-TRENE: terms for products sold and installed from 2 January 2025 and a later copy (distributor-hosted copies)
• Huawei, Smart PV Warranty Policy (European), 31 August 2026
• Tesla, Megapack 2 XL datasheet, Rev. 2.0, 13 November 2025 (copy hosted by Cayuga County, New York)

Related reading

• Commercial battery storage: a buying guide
• What UK commercial battery pages leave out
• How to compare commercial battery storage quotes