How this comparison works
Which Solar Battery Suits Which Home
Start with the situation, not the brand. These are the cases where the documents point clearly one way, and the cases where they do not.
| Your situation | What the documents point to | Why |
|---|---|---|
| Already own a compatible GoodWe hybrid inverter | GoodWe Lynx Home | Same-vendor battery and inverter is the simplest retrofit; check compatibility first. |
| Want to start small and add capacity later | Any of the three | Fox EP11 scales to 41.6 kWh, SigenStor adds 5.2 or 7.8 kWh modules, GoodWe goes to eight towers (131 kWh). Add matching modules from the same generation. |
| Want the longest written term | Fox ESS EVO or EQ (12 years); Sigenergy offers a 15-year extension | The others stop at 10. See the throughput section: the term is only half of the guarantee. |
| Heavy daily cycling (smart tariff, EV) | Fox ESS EP / EVO | Fox’s throughput floor is the highest relative to size, so the warranty lasts longest under daily cycling. |
| Exposed outdoor wall | Check the IP rating | SigenStor IP66, Fox EP11 IP65, GoodWe LX F IP55 (datasheets). All three are specified for outdoor use. |
| Power-cut backup matters | Specify it at design, on any brand | A grid-tied battery shuts down in an outage unless backup hardware is fitted. Ask whether backup is whole-home or essential circuits only. |
| Low electricity use, no smart tariff | Possibly none | The Energy Saving Trust says savings “won’t always be enough on their own to justify the cost”. Our battery storage installation page shows the numbers. |
Judgements are ours; the figures in the right-hand column are from the manufacturers’ documents. Energy Saving Trust, "Battery storage" (page last updated 6 October 2026)
Fox ESS, SigEnergy and GoodWe Compared on Their Own Documents
| Fox ESS | SigEnergy SigenStor | GoodWe Lynx Home F / F PLUS+ | |
|---|---|---|---|
| Units | EP5 (5.18 kWh), EP11 (10.36 kWh nominal, scalable to 41.6 kWh), EVO5, EVO10 all-in-one | BAT 5.0 (5.38 kWh total, 5.2 usable), BAT 8.0 (8.06 total, 7.8 usable) | LX F 6.6 / 9.8 / 13.1 / 16.4 (6.55 / 9.83 / 13.1 / 16.38 kWh usable), up to eight towers (131 kWh) |
| Ingress protection | EP11 IP65 | IP66 | IP55 (indoor and outdoor) |
| Term and retained capacity | EP 10 years; EVO and EQ 12 years; at least 70% of nominal energy, or the throughput floor | 10 years; 70% of usable energy (EU warranty) or the floor; extension to 15 years at 60%; one 2025 revision says 60% at ten | 10 years performance: 70% of usable energy or the floor; 5 years product warranty (global LX F document) |
| Throughput floor (manufacturer) | EP5 19.42 MWh, EP11 38.85 MWh, EVO5 23.99 MWh, EVO10 47.88 MWh | 15.85 MWh (5 kWh module), 23.77 MWh (8 kWh module) | LX F 6.6-H 16.77, 9.8-H 25.16, 13.1-H 33.54, 16.4-H 41.93 MWh |
| Company | Established UK distribution; current UK policy V4.4 (August 2025) | Founded 2022, Shanghai; SigenStor shown to the UK in October 2023 | GoodWe PLUS+ programme extends the hybrid-INVERTER warranty to 10 years |
Sources: Fox ESS Battery Warranty Policy, UK & Ireland (V4.4); Fox ESS EP11 datasheet V1.4; Sigenergy SigenStor warranty (EU); Sigen Battery datasheet; GoodWe Lynx Home F PLUS+ product page; GoodWe, warranty extension for hybrid inverters in 2026. Sigenergy’s server blocks automated downloads, so its terms are taken from extracts of its documents; confirm them against the current PDF.
Why a 10-Year Warranty Is Not 10 Years of Full Capacity
Every warranty in the table says the same thing in two parts: the battery keeps at least a stated share of its capacity (60–70%) for a stated number of years or until it has delivered a stated amount of energy, whichever comes first. The years are the headline. The energy is the limit that bites if you cycle the battery hard — which is exactly what a smart tariff or an electric car makes you do.
Dividing each manufacturer’s throughput floor by the energy it states gives the number of full cycles the guarantee covers. This is our arithmetic on their figures, not a manufacturer claim:
| Model | Throughput floor | Stated energy | Full cycles covered | Years at one cycle a day |
|---|---|---|---|---|
| Fox ESS EP5 | 19.42 MWh | 5.18 kWh | 3,750 | 10.3 years |
| Fox ESS EP11 | 38.85 MWh | 10.36 kWh | 3,750 | 10.3 years |
| SigenStor BAT 5.0 | 15.85 MWh | 5.20 kWh | 3,050 | 8.4 years |
| SigenStor BAT 8.0 | 23.77 MWh | 7.80 kWh | 3,050 | 8.3 years |
| GoodWe LX F 9.8-H | 25.16 MWh | 9.83 kWh | 2,560 | 7.0 years |
| GoodWe LX F 13.1-H | 33.54 MWh | 13.10 kWh | 2,560 | 7.0 years |
Full cycles = floor ÷ stated energy (nominal for Fox ESS, usable for SigenStor and GoodWe). One full cycle a day is the heaviest realistic domestic use; most homes cycle a battery less. Sigenergy’s floors come from extracts of its EU warranty.
Read it this way. A Fox ESS EP battery cycled fully every day reaches its floor after about 10.3 years, so the 10-year term is the limit. A SigenStor reaches it after about 8.3 years and a GoodWe LX F after about 7.0 — before the calendar does. Few homes cycle every day at full depth, so the gap is smaller in practice, but for a home on a smart tariff with an electric car it is the difference between a 10-year guarantee and a 7-year one. It is the single most useful number missing from most comparison pages.
What Each Brand Is, Without the Marketing
Fox ESS
Fox ESS’s UK and Ireland battery policy (version 4.4, 11 August 2025) gives EVO and EQ batteries 12 years and EP and CQ batteries 10 years, each at 70% of nominal energy or a throughput floor. The same policy says only the installer and Fox-authorised staff can make a claim, so the end user depends on the installer — a reason to ask who will still be around. The EP11 is rated IP65 and scales to 41.6 kWh by adding units in parallel. The older ECS range does not appear in the current UK policy table; if you already own one, ask the installer to check your warranty paperwork.
SigEnergy
Sigenergy is the newest of the three: founded in 2022, headquartered in Shanghai, with SigenStor unveiled to the British market at Solar & Storage Live in October 2023. The battery modules are 5.2 and 7.8 kWh usable and rated IP66. Its warranty is 10 years, extendable to 15 at a lower guaranteed capacity, and its own documents disagree on the retained-capacity floor (70% in the EU warranty, 60% in a 2025 Europe revision). That is worth asking about, not a reason to rule it out. Because the company is young, a warranty is a promise from a business with a short UK history.
GoodWe
GoodWe’s Lynx Home F range (usable 6.55 to 16.38 kWh, IP55) carries a 10-year performance warranty at 70% of usable energy or a throughput floor, plus a 5-year product warranty in its global document. Its PLUS+ programme is often described as a free 10-year warranty; what it extends is the hybrid inverter to 10 years, for PLUS+-qualified installers, where the battery is first operated by 31 December 2026. The battery itself is covered by the performance warranty above. Warranty claims are routed through the installer.
What about GivEnergy and Tesla?
GivEnergy Ltd entered administration on 9 April 2026, and a battery warranty depends on the company standing behind it, so we no longer fit it. Octopus lists the Tesla Powerwall 3 (13.5 kWh) at £7,999 battery-only, against £3,947 and £5,336 for its 5 and 10 kWh options. We do not fit Powerwall; our Fox ESS vs Tesla Powerwall page compares it with one we do.
What a Solar Battery Costs per kWh
Headline prices hide the useful number: what each extra kWh of storage costs.
Per-kWh figures are our division of the published prices by the stated capacity. Octopus Energy, battery-only installation (April 2026 prices, read 7 October 2026); Energy Saving Trust, "Battery storage" (page last updated 6 October 2026); HMRC VAT Notice 708/6, energy-saving materials and heating equipment. Octopus adds a £500 non-refundable advance payment. The marginal cost of the second 5 kWh is far lower than the first, so a larger battery is cheaper per kWh — but only worth buying if your home can use the extra energy, which our battery storage installation page shows it often cannot.
Best Solar Battery UK: Questions Answered
The questions we are asked most, answered against the documents.
There is no single best. The right battery depends on how much energy you use outside solar hours, whether it has to work with an inverter you already own, how much cycling you will put it through, and whether power-cut backup matters. The Energy Saving Trust says a typical home system might be 10 kWh, but in a home that uses about 6.8 kWh a day in total a smaller battery does the same job for less.
Read past the headline years. Every warranty here ends at the earlier of its term or a throughput floor. Worked out from the manufacturers’ own tables, a battery cycled fully once a day reaches that floor after about 10.3 years on a Fox ESS EP, about 8.3 on a SigenStor and about 7.0 on a GoodWe LX F. Fox ESS gives its EVO and EQ ranges 12 years; Sigenergy offers an extension to 15. None of them is a promise of full capacity for that long — each guarantees 60–70% of it.
On paper they differ in a few checkable places: Fox ESS EP units are rated IP65 and GoodWe’s LX F range IP55; the Fox EP throughput floor equals about 3,750 cycles against about 2,560 for GoodWe; GoodWe scales to eight towers (131 kWh) and Fox EP11 to 41.6 kWh. If your inverter is already a compatible GoodWe hybrid, the same-vendor battery is the simpler retrofit. See our Fox ESS vs GoodWe comparison for the head-to-head.
We cannot give you a sourced premium, because no published price list covers all three brands like for like — ask every installer to quote by usable kWh and compare. What is documented: Sigenergy was founded in 2022 and unveiled SigenStor to the UK in October 2023, so it has the shortest UK track record of the three, which matters because a warranty is only as good as the company behind it.
No battery carries an MCS approval — the MCS product directory has no battery category, so a claim that a particular battery is “MCS approved” cannot be checked. MCS certifies installers (to MIS 3012 for batteries). To check a battery, look up the exact model and firmware on the ENA type-test register, which is what the network operator relies on.
Match it to the energy your home uses outside solar hours, not to the roof. Doubling the battery does not double the saving: in a medium-use home a second 5 kWh adds nothing, because there is nothing left to displace. Our guide to what size solar battery you need works through it with Ofgem’s typical household figures.
Usually, but compatibility depends on your inverter. An AC-coupled battery has its own inverter and leaves your system untouched; a hybrid-inverter swap replaces the old inverter. We check before recommending anything.
Where these figures come from
Every figure above comes from a published source or from arithmetic on one. Read 7 October 2026. Where a source updates, the page should be re-read before a figure is reused.
- Fox ESS Battery Warranty Policy, UK & Ireland (V4.4) — EP5 and EP11 10 years, EVO 12 years; at least 70% of nominal energy or a throughput cap, whichever comes first; EP11 10.36 kWh nominal, 38.85 MWh cap (about 3,750 full cycles)
- Fox ESS EP11 datasheet V1.4 — EP11 nominal energy 10.36 kWh, scalable to 41.6 kWh, IP65, 100% depth of discharge
- Sigenergy SigenStor warranty (EU) — 10-year battery warranty; 70% of usable energy at 10 years or a throughput floor, whichever first; extension to 15 years at 60%
- Sigen Battery datasheet — BAT 5.0 5.38 kWh total / 5.2 kWh usable; BAT 8.0 8.06 kWh total / 7.8 kWh usable; IP66; -20 to 55 C
- GoodWe Lynx Home F PLUS+ product page — usable energy 6.55 / 9.83 / 13.1 / 16.38 kWh; LFP; IP55; up to eight towers in parallel (131 kWh)
- GoodWe, warranty extension for hybrid inverters in 2026 — Lynx F / F PLUS+ batteries carry a 10-year product and performance warranty; the PLUS+ programme extends the HYBRID INVERTER warranty to 10 years when installed by a GoodWe PLUS+ installer and the battery is first operated between 15 May 2023 and 31 December 2026
- Octopus Energy, battery-only installation (April 2026 prices, read 7 October 2026) — 5 kWh £3,947; 10 kWh £5,336; Tesla Powerwall 3 £7,999; £500 non-refundable advance payment
- Energy Saving Trust, "Battery storage" (page last updated 6 October 2026) — typical lifespan 10 to 12 years; 5 kWh around £4,600, range £1,500 to £10,000; typical system 10 kWh; savings "won't always be enough on their own to justify the cost"; stored energy is less efficient than direct use
- HMRC VAT Notice 708/6, energy-saving materials and heating equipment — zero rate for installation to 31 March 2027, 5% from 1 April 2027; batteries qualify on their own from 1 February 2024
- ENA type-test register (Connect Direct) — records compliance per model AND firmware version
- Ofgem typical domestic consumption values, from 1 July 2026 — 1,600 / 2,500 / 3,800 kWh a year (low / medium / high)
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