Marstek Venus E 4.0 UK: Is This 5kWh Battery Legal?

The Marstek Venus E 4.0 is a 5 kWh lithium iron phosphate home battery that has just reached the UK through Marstek's local distribution network, and it is being sold with a "plug and play" pitch. That wording invites an obvious question after August's plug-in solar rule change: is it a legal plug-in battery? Not in the sense most buyers will assume. Plug-in solar became legal in Great Britain on 27 August 2026, but plug-in batteries were excluded, and the UK retailer listings for Marstek's earlier Venus E 3.0 say the unit must be hardwired by a qualified electrician. Here is what the Venus E 4.0 is, what it costs, and how it can legally be installed.

What is the Marstek Venus E 4.0?

It is a compact, floor-standing AC-coupled battery. In other words it connects to your home's mains wiring through its own built-in inverter, rather than sitting on the DC side of a solar array. That makes it suited to homes with existing solar, or to households simply wanting to buy cheap off-peak power and use it later. For the wider picture, see our guide to home battery storage.

The specifications published by pv magazine's hands-on look at the unit shown at Solar & Storage Live UK are:

Marstek also sells a 2 kWh Venus E Mini and a 10 kWh Venus E Max in the same range. The pv magazine piece does not state a warranty or price for the 4.0, so treat any figure you see elsewhere as the retailer's claim until Marstek confirms it.

Is the Venus E 4.0 a legal plug-in battery in the UK?

No: plug-in batteries are not yet covered by any UK rule change. The government's plug-in solar framework allows 800 W AC kits that you can self-install, but batteries were left out. The Department for Energy Security and Net Zero (DESNZ) has instead tendered a safety and risk assessment of self-installed plug-in batteries rated up to 800 W AC, and the Energy Storage Association has warned that plug-in batteries installed without wiring and consumer-unit checks "would not meet current standards".

The Venus E 4.0 also sits well above that 800 W ceiling: it is a 3 kVA unit. So even if the plug-in battery rules arrive as expected, this product would not fall inside them. Our explainer on why plug-in batteries won't be UK-legal until at least 2028 covers the timeline in more detail.

What the UK distributors do instead is sell it as a conventional battery. The UK listing for the Venus E 3.0 at MarstekDirect states that the unit ships with a European output socket but, "due to current UK standards", must be hardwired into a dedicated circuit or a fused spur connected directly to the consumer unit by a suitably qualified electrician. It describes the unit as G98 compliant and carrying an Energy Networks Association (ENA) reference. Check that the 4.0 you are quoted carries the same, because we could not find a UK product page confirming it for the 4.0 specifically.

How it has to be installed

In practice, buying a Venus E 4.0 means treating it like any other home battery:

• Use a qualified electrician. Hardwiring to a dedicated circuit or fused spur is installation work, not a plug-in job. Our home battery installation guide covers what to expect on the day.
• Notify your network operator. Grid-connected batteries that can export need to be registered with the distribution network operator. Our G98 notification guide explains the process.
• Mind the location. From 15 October 2026 the new BS 7671 battery rules ban loft installations for new domestic installs, so a ground-floor utility room or garage is the realistic home for a 47 kg cabinet. See why home batteries can't go in lofts.
• Check your insurer. An uncertified self-install can complicate a claim, so keep the electrician's certificate.

The upshot: the "plug and play" label describes the app set-up, not the electrical connection. Skipping the electrician would leave you with an installation that does not meet current UK standards.

How much does the Venus E 4.0 cost in the UK?

At the time of writing, one UK retailer listed the Venus E 4.0 at £1,499.99 but marked it as sold out, while the Venus E 3.0 (5.12 kWh) was listed at £1,399.99 with a 10-year warranty. European listings show the 4.0 at €1,649 including VAT. Add the electrician's visit and any DNO paperwork on top, and a realistic all-in cost is higher than the sticker price. Prices and stock are moving quickly with a new launch, so confirm before ordering.

Whether a 5 kWh unit is the right size for you depends on your daily use; our guide to what size home battery you need walks through the sums.

Octopus integration: not there yet

Marstek's key account manager told pv magazine the company is "working on deeper integration with Octopus Energy and other energy management providers", but did not say the work is finished. If you rely on a smart tariff to schedule charging automatically, that gap matters: until integration lands you may need to manage charge windows yourself via Marstek's app or a third-party energy manager. For a sense of where Octopus is heading, see our Octopus Nook battery range article.

Should you buy one now?

It is a reasonable buy only if you are happy to treat it as a standard hardwired battery. The hardware specification is competitive for a 5 kWh LiFePO4 unit, and the price undercuts many installer-led systems. Against that, you are buying from a newer distribution channel, the 4.0's UK compliance paperwork is unconfirmed, and the smart-tariff integration is still in development. If you want a fully supported package with a long installer-backed warranty, compare quotes from an MCS-certified installer first.