The short answer
The "Fox Cube" is Fox ESS's ECS battery — "Energy Cube" is Fox's own name for the family — and it is what sits in both of the Fox jobs we filmed. It is a modular, high-voltage, floor-standing stack you size in blocks, and it does the job well. It is also the previous generation: ECS is not on Fox's current UK residential range page and is not in the current UK and Ireland battery warranty policy, so a new Fox stack from us today is an EQ.
For the record, we install Fox ESS battery and hybrid-inverter systems (including the Fox Cube battery) and have two complete installs documented on our YouTube channel. Andy Pemberton surveys and specifies every system we quote.
Cube, ECS, EQ: which product are you reading about?
The only Fox document that uses the word is Fox's own ECS4000 user manual for the US market, titled "Energy Cube User Manual". Neither "ECS" nor "Energy Cube" appears on Fox's current UK residential range page, so Cube is owner-and-installer shorthand rather than a catalogue name. That page lists three battery families — EQ, EP and the CQ7 at 7.02 kWh per module — plus the Evo AIO, PowerQ AIO and MiniQube all-in-ones. No ECS.
That matters for one reason: the current UK and Ireland battery warranty policy names every product it covers — the EP and CQ models, the whole EQ range, EVO5 and EVO10 — and ECS is not among them. If you already own a Cube, the warranty that applies is the one in force when it was installed; we will not print a term, because no current Fox document states one. If you are offered a "new" Cube in 2026, ask for the model number and the warranty document first.
Module capacities, stacking and where it goes
Both Cube models build the same way: a manager module at the bottom, support modules above, all in series on one footprint. Fox's ECS2900 datasheet (v3.7, April 2025) gives 2.88 kWh per module — not 2.9. The ECS4100 datasheet (v3.5, December 2023) gives 4.03 kWh per module, "scalable to 28.21 kWh".
| Fox Cube (ECS) | Per module | Two modules | Maximum stack |
|---|---|---|---|
| ECS2900 | 2.88 kWh | 5.76 kWh | 20.16 kWh (7 modules) |
| ECS4100 | 4.03 kWh | 8.06 kWh | 28.21 kWh (7 modules) |
Both are lithium iron phosphate at 90% depth of discharge, with a quoted cycle life of at least 6,000 cycles. Do the usable-energy sum before comparing: at 90% DoD a two-module ECS4100 is roughly 7.25 kWh usable (our arithmetic from Fox's figures), not the nominal 8.06 kWh. Where our older video titles round that differently, take the datasheet.
Siting is settled by weight and clearance, not the IP rating — both are IP65. The ECS2900 is 570 mm wide and 380 mm deep, but a two-module stack weighs 68.3 kg, and 75.5 kg for the ECS4100 equivalent, climbing with every block. Fox's current UK battery warranty policy requires 300 mm of clearance around the pack and an ambient between -10°C and 50°C, which is the standard we site every stack to. So: floor space with air around it, and a route through the door two people can manage.
What a new Fox stack looks like today
Buy now and you are buying EQ. On a single-phase H1-G2 or K Series inverter:
- EQ2900 — 2.88 kWh per module, 2 modules (5.76 kWh) to 7 (20.16 kWh). The same block size as the ECS2900 Cube.
- EQ4800 — 4.66 kWh per module, 2 modules (9.32 kWh) to 9 (41.94 kWh).
- EQ5000 — 4.92 kWh per module, 2 modules (9.84 kWh) to 6 (29.52 kWh).
The EQ4300 is missing on purpose: Fox's UK stack table and Fox's own global datasheet disagree on its per-module figure, and we will not print a number the manufacturer contradicts.
Fox lists the EQ range as high voltage, modular, IP65, 90% depth of discharge, floor-mounted, naturally convection-cooled, with a battery warm-up function and a 12-year warranty. Read that warm-up line twice: it is not available on the EQ4800, and elsewhere works only when the system has both master and slave units. Round here batteries often end up in an unheated garage, so that sentence picks the model more often than capacity does.
The inverter is half the product
A Cube or an EQ is a high-voltage DC stack that does nothing on its own. The hybrid inverter decides what the system can do.
The single-phase H1-G2 and AC1-G2 come in 3, 3.7, 5 and 6 kW: dual MPPT, 200% PV oversize ratio, DC or AC coupled, smart tariff compatible, IP65, paired with the EP, EQ and CQ7 batteries. Fox's datasheet (v2.2, June 2026) adds the numbers that matter on site: battery voltage 80–480 V, maximum battery charge and discharge current 40 A, EPS switch time under 10 ms, G98, G99 and EN 50549 grid regulation, wall-mounted at 22 kg. The H1-5.0-E-G2 takes 10,000 Wp of array for 5,000 W rated output at 97.08% peak efficiency, and the 3.7 kW model is footnoted "3680 for G98".
That 40 A battery current limit is the spec people skip and then regret. It caps how fast the stack fills or empties however many modules you bolt on, so if the plan is to fill the battery inside a cheap overnight window, size for the charge rate, not just the array. Bigger arrays step up to the KH and KA Series: 7, 8, 9 and 10 kW with 3 or 4 MPPTs, installable DC coupled, AC coupled, or battery-ready with no battery at all.
Warranty, and the clause that quietly costs five years
Battery cover under the current UK and Ireland policy (v4.5, September 2025): the whole EQ range plus EVO5 and EVO10 get 144 months from installation, but no more than 149 months from the date of manufacture — that manufacture cap is why we ask how long a battery has sat in a warehouse. The EP models and the CQ6 and CQ16 get 120 months, capped at 125 from manufacture.
The performance side warrants at least 70% of nominal energy for that term or until a minimum energy throughput, whichever comes first: 12.15 MWh on the EQ2900, 17.47 MWh on the EQ4800, 18.45 MWh on the EQ5000. Cycle hard on a cheap-rate tariff and throughput ends the warranty before the calendar does.
Inverters are separate: 60 months from installation, capped at 65 from manufacture, with a further 60 months free — ten years in total — for the listed series including the hybrids, but only if the warranty is registered on Fox's website before 36 months from the date of manufacture and the device is registered to Fox Cloud using a Fox datalogger. Skip either and you have handed back five years of cover. Registration is at warranty.foxesscloud.com; inverter and battery warranties go in separately.
Under the policy only the installer and Fox's own authorised personnel can claim, and installation by a non-accredited installer sits in the exclusions — though Fox states accreditation is not required. We are MCS Certified and NAPIT Registered, we register both warranties on what we fit, and we pass you the certificates.
FoxCloud, tariffs and Capture AI
FoxCloud runs in a browser and syncs with the Fox ESS app: real-time performance, battery health, trends by day, week, month or year, and the charge and discharge schedule. For tariffs there is a Manual Tariff mode with up to 96 slots and a one-click Smart Tariff, with Octopus, OVO, Kraken, E.ON and Hive shown as partners.
Capture AI predicts your consumption and generation, charging when electricity is cheapest and discharging at peak. Fox says it works with all suppliers and tariffs in the UK, is included free of charge with all Fox ESS systems, and that optimisation savings are 100% yours, with Capture taking a share only of grid-services earnings. Included rather than sold as a subscription is a point in Fox's favour.
FoxCloud 2.0, announced on 6 February 2026, adds a five-second data refresh and an AI Mode that learns from habits, weather and tariff data — though Fox notes certain features will not be available during the initial release.
Our take from installing them
Two complete Fox jobs are documented end to end: a 9.6 kW solar array with a Fox Cube battery in Ingleby Barwick, and a Fox Cube battery with JA Solar panels on a garage roof. What we would take from both:
- The stack goes together quickly; the day is decided elsewhere. Modules land on the base and link in series, and that part is fast. The consumer unit, the cable route, the isolation and the network operator paperwork set the length of the day.
- Garage roofs are a solved problem. The second video exists because the house roof was not the right place for the array. If yours is shaded or the wrong pitch, an outbuilding is often the better plane.
- Floor space, not wall space. People expect something that hangs on a wall. A Cube, and an EQ after it, is a floor-standing stack needing clearance — settle that before survey day.
- Commissioning is not the finish line. Registration, the datalogger and getting the tariff schedule right are what turn hardware into the thing you paid for.
We are not publishing generation or savings figures from either job: we did not instrument them well enough for those numbers to mean anything.
Who it suits, and who should buy something else
It suits you if you want a stack you can start modest on and extend later, if you are having new solar and would rather one manufacturer supplied both inverter and battery, and if you have the floor space.
Buy something else in three cases. If you want one sealed box on a wall and no decisions, a Powerwall 3 is the tidier answer — the two are side by side in Fox ESS vs Tesla Powerwall 3. If you want DC car charging inside the same stack, that is a SigenStor conversation, covered in Sigenergy vs Fox ESS. And if you have no floor to give up, Fox's own MiniQube is a different product for that problem: plug-in storage from 2.11 kWh to 10.55 kWh in 2.11 kWh modules, pitched at apartments and retrofits.
Fox announced in May 2026 that S&P Global's tracker ranked it number one in the UK for residential storage shipments by MWh in 2025 — Fox's figure, not our measurement. And since Fox does not sell direct, whoever fits it is who you deal with for the next decade.
Getting one fitted
No Fox page publishes UK prices and we are not going to invent a range. The figure depends on stack size, which inverter it sits behind, whether backup is in scope, and what your consumer unit and cable route need. Ask us for a fixed price after a free survey and compare it on matching spec.
We install across Teesside, County Durham and North Yorkshire from our base in Yarm. How far we travel depends on the job — just ask.
Send your postcode through our contact page and Andy will come back with a configuration and a number. More reading: the Fox ESS installer page, our hybrid inverter review, what a Fox ESS battery costs, battery storage and solar panels across Teesside.