The short answer
We fit both, so this is not a pitch for one of them. Tesla Powerwall 3 is the simpler, more powerful box: one unit, 13.5 kWh usable, a solar inverter built in, and the strongest whole-home backup we install. Fox ESS is the flexible, lower-cost route: a hybrid inverter plus a battery you size in modules, from 5.76 kWh up.
The honest answer is that they are not chasing the same customer. If riding out a power cut is the point of the project, Powerwall 3 is the one. If budget is the binding constraint, or you want to start battery-ready and add storage later, Fox usually makes more sense.
Everything below comes from Tesla's and Fox's own UK documents and from fitting them. See also our Powerwall 3 review and Fox ESS hybrid inverter review.
Fox ESS vs Tesla Powerwall 3 at a glance
One warning: Tesla's 13.5 kWh is a usable figure, while Fox quotes nominal energy and rates the EQ range at 90% depth of discharge.
| Tesla Powerwall 3 | Fox ESS | |
|---|---|---|
| Capacity per unit | 13.5 kWh usable, one size only | EQ2900 2.88, EQ4800 4.66, EQ5000 4.92 kWh; EP6 5.76, EP12 11.52 kWh; CQ7 7.02 kWh |
| How it scales | 13.5 kWh steps: up to 4 units plus 3 Expansions, to 94.5 kWh | A module at a time: EQ2900 5.76–20.16, EQ4800 9.32–41.94, EQ5000 9.84–29.52 kWh |
| Continuous power | 3.68–11.04 kW at 230 V single phase; 44 kW across a multi-unit system | Set by the inverter: H1-G2 / AC1-G2 3–6 kW, KH / KA 7–10 kW |
| Backup | Backup Gateway 2, whole-home or partial, 185 A load start | Inverter EPS under 10 ms; whole-home needs the EPS-BOX-SP gateway, 2–3 seconds |
| Warranty | 10 years, 80% retention, unlimited cycles for self-consumption, time-based control and backup | EQ 144 months, EP 120 months, to 70% of nominal or a throughput cap; inverters 60 plus 60 months |
Capacity: one block, or a stack you build
Powerwall 3 is 13.5 kWh of usable energy and comes in no other size. Need more and you add another Powerwall 3 or a Tesla Expansion unit, each a further 13.5 kWh, to a maximum of seven units, 94.5 kWh and 44 kW of continuous AC power.
Fox works the other way round: pick the hybrid inverter, then build the battery from modules. On the single-phase H1-G2 and K Series an EQ2900 stack runs from two modules (5.76 kWh) to seven (20.16 kWh); EQ4800 modules are 4.66 kWh each up to nine (41.94 kWh); EQ5000 modules are 4.92 kWh up to six (29.52 kWh).
That granularity matters more than the datasheets suggest. On a three-bedroom house with a modest array, 13.5 kWh is often more than the roof will fill between October and February, so you pay for capacity that sits half empty. Fox lets you buy what the house actually cycles — though at 20 kWh and above, a Powerwall and an Expansion is fewer components and fewer connections.
Power and backup: what happens when the lights go out
This is where they genuinely separate. Tesla's UK datasheet lets the installer configure Powerwall 3's output at 230 V single phase from 3.68 kW to 11.04 kW, with 185 A LRA load start. An ordinary Teesside semi keeps running through a cut, and a heat pump will still start.
UK backup uses Backup Gateway 2, the supported islanding device on the UK datasheet, and whole-home or partial-home backup is set at design stage. A Non-Backup configuration swaps the Gateway for a Tesla Remote Meter to cut the upfront cost: no backup power, no Storm Watch or Backup Reserve, though a Gateway can be added later. Our Backup Gateway guide covers it properly.
Fox does it in layers: the hybrid inverter's own EPS switches in under 10 milliseconds, covering an essential-loads circuit, and whole-house backup adds the EPS-BOX-SP gateway, which isolates the property on grid loss and restores power from battery and solar after a typical changeover of 2 to 3 seconds. Powerwall gives more power and a transition you barely notice; Fox is the cheaper way to keep the fridge and the router alive.
One box or two: the inverter question
Powerwall 3 has the solar inverter inside it: three solar inputs and three MPPTs, a maximum solar input of 20 kW STC, and 97.5% solar to home or grid (89% solar to battery to home or grid). One box, one commissioning, one warranty.
Fox splits it. The H1-G2 / AC1-G2 single-phase range comes in 3, 3.7, 5 and 6 kW, dual MPPT with a 200% PV oversize ratio, DC or AC coupled and IP65 rated; the KH / KA Series covers 7 to 10 kW with three or four MPPTs and can be fitted battery-ready, so you install now and add storage later.
Two boxes need more wall space and two warranties to track, but a separate inverter is cheaper to replace, and AC coupling lets Fox sit alongside an inverter you already own. Tesla retrofits too: Powerwall 3 can be added to existing solar and is compatible with all major solar inverter brands, but never to a Powerwall 2.
Warranty: 12 years is not automatically better than 10
Fox's headline number is longer, and it still does not settle the argument.
Tesla warrants Powerwall 3 against defects for ten years from installation, guaranteeing 13.5 kWh on day one and 80% energy retention at ten years in the UK, with unlimited cycles for solar self-consumption, time-based control and backup; other applications are capped at 37.8 MWh. The condition people miss is connectivity: Tesla's EMEA manual says the warranty may be limited to four years if the system is not kept online.
Fox splits it in two. Under the UK & Ireland battery policy v4.5 the EQ range carries 144 months from installation and the EP range 120 months, both to at least 70% of nominal energy or a minimum energy throughput, whichever comes first: 12.15 MWh for an EQ2900 module, 43.19 MWh for an EP12. That policy also requires 300 mm of clearance around the battery for cooling. The inverter is separate again — 60 months under Fox's policy v1.8, plus 60 free on the hybrid and AC series if it is registered on the Fox website within 36 months of manufacture and to Fox Cloud with a Fox datalogger.
So Fox gives more years on the battery; Tesla a higher floor, 80% rather than 70%, and no throughput cap for ordinary home use.
Apps, tariffs and living with it
The Tesla app is the more polished. Savings mode charges when your supplier's energy is cheap and runs the house when it is expensive; Backup Reserve holds a share back for outages; Storm Watch charges to maximum on a Met Office amber or red alert mentioning a risk of power cuts. Intelligent Octopus Flux enrols Powerwall in a virtual power plant that Octopus manages.
FoxCloud beats Tesla on manual control: up to 96 tariff slots you set yourself alongside a one-click Smart Tariff, with Capture AI included free of charge on all Fox ESS systems. FoxCloud 2.0, announced on 6 February 2026, adds a five-second data refresh and an AI Mode that learns from energy habits, weather forecasts and tariff data.
If you like tinkering, Fox gives you more dials. If you want to set it and forget it, Tesla does more without being asked.
Our take from installing them
We are a Tesla Certified Installer, one of around 50 in the UK by our own count. We install Fox ESS battery and hybrid-inverter systems, including the Fox Cube battery, and have two complete installs documented on our YouTube channel: a 9.6 kW array with a Fox Cube battery in Ingleby Barwick, and a Fox Cube with JA Solar panels on a garage roof. Our own solar-and-Powerwall job runs to three parts on the same video page.
Two things you only learn on site. Powerwall 3 is 130 kg and goes in as one piece; Fox EQ modules go in one at a time and stack, which is often the difference between a battery fitting a tight utility room and not. And Tesla says a typical install is a full day with the power off four to six hours, up to eight or more if extra electrical work is needed, so we book early and warn the household.
One thing to be straight about on the Fox side: the Fox Cube in our films is Fox's ECS or Energy Cube generation, which no longer appears in Fox's current UK residential range or in the covered-product list of the current UK & Ireland battery warranty policy. Those systems are covered by the warranty in force when they went in, but a new Fox quote from us is built on the EQ range. More in our Cube review.
Who should choose which
Powerwall 3 is the right call if
- Backup is the reason you are buying: 11.04 kW and 185 A load start covers a real house, not a lighting circuit.
- You want inverter and battery in one unit, with 20 kW of solar input to grow into.
- You are sizing at 13.5 kWh or more and want the least fiddling.
Fox ESS is the right call if
- You want to buy the capacity you actually cycle, starting around 5.76 kWh.
- You want to add storage a module at a time as your usage changes.
- You want a battery-ready inverter now and the battery next year.
Where each is the wrong answer
Powerwall is wrong if 13.5 kWh is more than the house will ever use, or if budget is the binding constraint. Fox is wrong if you want the least kit on the wall or the most seamless changeover in a cut. We have talked customers out of both; the Sigenergy comparison covers the third system we install.
What they cost, and getting one fitted here
Neither manufacturer publishes a UK price: Tesla's order page connects you to a Tesla Certified Installer who contacts you about pricing, and Fox pairs you with a partner installer. Anyone quoting a manufacturer RRP is quoting themselves.
Our own guidance, and this is ALPS's figure rather than Tesla's: Powerwall 3 from £8,500 installed, depending on the property, the electrics and whether it goes in with new solar. For Fox it depends on the inverter and the number of modules, so ask us for a fixed price after a survey. Andy surveys and specifies every system we quote. HMRC's VAT Notice 708/6 zero-rates installation of specified energy-saving materials until 31 March 2027, batteries included since 1 February 2024.
We install across Teesside, County Durham and North Yorkshire from our base in Yarm. How far we travel depends on the job — just ask. We are MCS Certified and NAPIT Registered, with 500+ five-star reviews across Checkatrade and Google. Start on the Fox ESS installer page or the Tesla Powerwall installer page, or our regional pages for Teesside and County Durham and North Yorkshire; battery storage covers the rest. Send us your postcode and we will tell you which of the two we would fit, and why — get in touch or use the form below.