Fox ESS batteries in the UK: prices, models and warranty

The Fox ESS range, in two families

Fox ESS, the brand of Foxess Co., Ltd of Wuxi in China, sells two kinds of home battery in the UK, and they are warranted differently.

• EVO: battery and inverter in one box. The EVO 10 holds 10.24 kWh of lithium iron phosphate cells alongside a hybrid inverter and charger, in versions rated from 5 kW to 10 kW. The EVO 5 holds 5.12 kWh. Octopus fits a Fox EVO 10 with a 5 kW inverter in its larger solar package, and a Fox EVO at both of its battery-only sizes.
• EP and other modules: battery only. EP batteries (EP5 5.18 kWh, EP6 5.76 kWh, EP11 10.36 kWh, EP12 11.52 kWh) pair with a separate Fox inverter. Octopus’s entry-level solar package uses a Fox ESS H1 3.7 kW inverter with an EP 5.18 kWh battery. Octopus describes that package as carrying a 12-year warranty for the inverter and battery, two years longer than Fox’s own term for EP batteries, so ask who covers the difference; Octopus’s packages and terms are set out on our Octopus page.

An all-in-one is simpler to install and needs less wall space; a separate inverter and battery lets each part be replaced on its own. That matters more than it sounds, because Fox’s battery warranty does not cover inverters, including the one inside an all-in-one.

What Fox ESS batteries cost

Octopus’s £5,336 for about 10 kWh works out at roughly £521 per kWh of rated capacity for an EVO 10, or about £550 per usable kWh. The official median for MCS-certified batteries of 6 to 11 kWh fitted in 2025/26 was £890 per kWh, so Octopus’s published price sits well below it. Large suppliers’ packaged prices often do, which is why this site’s quote checker marks them as low rather than typical. An independent installer’s quote for the same battery will usually be higher, and the checker shows whether it is within the normal range.

Installed home batteries carry 0% VAT until 31 March 2027, so a quote should not add VAT to the battery or its installation.

The solar battery cost guide shows what the average installation of each size cost in 2025/26.

EVO 5 or EVO 10: usable energy, price per kWh and payback

The two EVO sizes are labelled by nominal capacity, 5.12 kWh and 10.24 kWh. Fox quotes a 95% depth of discharge, so the energy you can use is about 4.86 kWh and 9.73 kWh. At Octopus’s published installed prices of £3,947 and £5,336 that is about £812 and £548 per usable kWh, so the larger battery costs a third less for each kWh of storage. This site’s model shows what that means for the saving, for a London home using 3,000 kWh a year:

The second 5 kWh costs £1,389 more and adds between £135 and £279 a year, so in all three set-ups the EVO 10 repays faster. The EVO 5 earns its place in a small home or as a first module, but not on price per kWh. Paybacks are simple (price divided by saving) and ignore the battery losing capacity; the calculator runs your own usage.

The no-solar rows come from this site’s model; the battery-only page tests Agile against 12 months of real prices.

What an EVO costs without installation

Five UK retailers listed the EVO 10 with a 5 kW inverter on 7 October 2026 at between £2,880 and £3,356 before VAT, supply only, which is £3,456 to £4,027 with the standard 20% VAT. The five are Solareon (£3,098.60 before VAT), The Eco Supermarket (£2,880), AIZO Quality Heating (£3,158.33), ITS Technologies (£3,192) and Solar Trading UK (£3,355.80). Set against Octopus’s £5,336 for an installed battery of about the same size, the hardware at retail is about 54% to 63% of the price. An installed battery in a home is zero-rated for VAT until 31 March 2027; one bought without installation is not.

The rest of an installed price pays for fitting, commissioning, the network notification, the certification paperwork and the supplier’s margin, though a large installer buys in volume and pays less than a retail listing. Our article on Fox ESS EVO hardware prices against installed prices sets out each listing and what a quote should itemise.

The warranty: years, 70% and a throughput cap

Fox ESS’s UK and Ireland Battery Warranty Policy (version 4.5, 11 September 2025) promises at least 70% of a battery’s nominal energy for the warranty term or until a set amount of energy has passed through it, whichever comes first. The cap turns into a number of full cycles when you divide it by the battery’s size.

At exactly one full cycle a day, an EP battery reaches its cap after about 10.3 years and an EVO after about 12.8, so the cap and the calendar term end at about the same time. The catch is that a battery on a time-of-use tariff with solar can do more than one cycle a day in summer: charging overnight, emptying in the morning, refilling from the panels and emptying again in the evening peak. At 1.5 cycles a day, the EVO 10’s cap arrives after about 8.5 years.

The workmanship term runs from installation, but with a limit from manufacture: 120 months from installation and no more than 125 from manufacture for EP and CQ models, and 144 and 149 months for EVO and EQ models. A battery that sat in a warehouse for a year before it was fitted therefore has a shorter warranty than the headline.

Conditions that can void it

• The battery must run between −10°C and 50°C ambient for the performance warranty to hold.
• Installation by a non-accredited installer, inadequate ventilation, or unauthorised repair or reinstallation are excluded.
• The policy says a clearance of at least 300 mm must be left around the battery pack for cooling, which affects where it can go in a cupboard or garage.
• If a model is no longer sold, Fox may replace it with an alternative of equivalent function and performance.

How a Fox ESS claim works

This is the part of the policy that matters most after the GivEnergy administration. Fox’s policy says the only people who can claim are the installer and Fox ESS authorised staff. The installer reports the fault, submits a returns form with evidence, and Fox commits to approving and dispatching a replacement within three working days, subject to stock.

If your installer has gone into administration or is insolvent, the policy lets the owner appoint a local installer to act instead, at the owner’s expense. Your statutory rights are unaffected, and Fox’s policy says so. The practical lesson is that the installer’s own guarantee and financial health matter as much as the manufacturer’s: check the installer’s workmanship warranty, its insurance-backed guarantee, and whether it will still be trading in year eight. Our guide to choosing a battery installer covers those checks.

Where Fox ESS fits

Fox EVO batteries suit homes adding a battery alone or with new solar, where the built-in hybrid inverter replaces a separate solar inverter. In a retrofit to an existing solar system, check whether the quote keeps your current inverter, which makes the system AC coupled, or replaces it. See adding a battery to existing solar. A 5 kW or larger EVO inverter on a single-phase home is above the G98 limit of about 3.68 kW, so expect the installer to apply to the network under G99.

Octopus pairs its Fox packages with Intelligent Octopus Flux, which lets Octopus control the battery, but that tariff is currently open only to customers who bought solar and a battery from Octopus. With a Fox battery from another installer, standard Octopus Flux (with solar) or an overnight tariff are the usual choices; see the best tariff for a home battery.

What standard Octopus Flux pays in each region is on the Octopus Flux rates page.

For backup, the EVO’s emergency output switches over in under 4 milliseconds; what that output can run, and what island-mode wiring adds to a quote, is on the power-cut backup page.

Checking a Fox ESS quote

Ask which model it is (EVO or EP, and the inverter rating), the battery’s nominal and usable capacity, the separate inverter warranty term, and who handles a warranty claim if the installer stops trading. Then compare it with at least one other brand. The Tesla Powerwall 3 and Enphase IQ Battery 5P pages set out the alternatives, and comparing two or three battery storage quotes on the same lines shows whether a Fox price is fair.