EcoFlow STREAM vs Anker Solarbank 4 Pro in the UK

The two batteries at a glance

On paper they’re close to twins. Each is a 5 kWh lithium iron phosphate (LFP) battery with its own inverter, four solar inputs adding up to 5,000 W, room to stack more batteries on top, and a 10-year warranty. The differences are in the price, the output, the box and the small print.

EcoFlow still sells its original STREAM range too, such as the 3.84 kWh STREAM Ultra X at £1,259. They were designed for Europe’s balcony market. In Great Britain the same hardwiring rule applies, so the electrician’s bill is a much bigger slice of the cost on a smaller battery.

Specs side by side

Here’s how they compare on the numbers that matter in a UK home. Where a figure comes with a condition, I’ve said so.

From Anker and EcoFlow’s UK product pages, checked 27 October 2026.

Two rows matter more than they look. The 60 V ceiling on the solar inputs decides which panels you can use, and I come back to it below. And the Anker’s 800 W default is a European plug-in setting, not a UK one. One more for the small print: EcoFlow rates its 10,000 cycles down to 60% of the battery’s original capacity, so read the warranty terms rather than the cycle count.

What they cost to get running

The price on the box isn’t the price of a working battery. You need a meter clamp so the battery can see what the house is doing, and an electrician to wire it in. These are the prices in each company’s UK shop as I write.

Then there’s the electrician. Owners have been posting quotes of roughly £375 to £1,500 to fit a Solarbank 4 Pro, with a cluster around £500 to £750, and the STREAM is the same job. That usually covers a new circuit with its own RCBO, an isolator, the cable run (often armoured cable to an outside wall), fitting the meter clamp, testing, the certificates and the G98 notification. If your consumer unit is full or past it, a replacement typically adds £500 to £1,200, and more if the earthing needs work.

The VAT trap

This is the bit that catches people out. HMRC’s VAT Notice 708/6 zero-rates the installation of home batteries until 31 March 2027, and that includes a standalone battery charged from the grid. From 1 April 2027 the rate goes to 5%. The catch is that energy-saving materials supplied without installation are standard-rated. Buy either battery from Anker’s or EcoFlow’s website and you’ve paid 20% VAT on the box, even if an electrician fits it the next day.

Have an installer supply and fit it as one job and the box is zero-rated too. That’s worth £283 on the Anker and £300 on the STREAM 5000 at its list price. One UK installer is already advertising a fitted 5 kWh STREAM from £2,499 all-in, a little under what you’d pay buying the box yourself and adding a mid-range fitting quote. If you’re weighing up timing, I’ve worked through what the 5% VAT rate from April 2027 really costs.

Solar inputs and the 60 V catch

Both batteries have four solar inputs that take up to 1,250 W each, but no more than 60 volts. That’s built for one panel per input, or two or three wired in parallel. It’s nothing like a normal rooftop system, where ten or so panels are wired in series into a string that runs at a few hundred volts.

So if you already have panels on the roof, you can’t move that string onto either battery. The battery charges from your surplus on the AC side instead, using its meter clamp to spot when you’re exporting. That’s exactly what the £1,599 STREAM AC 5000 is for, and the Anker can do the same with its Smart Meter Gen 2. Price either one against a conventional AC-coupled battery, though; my best solar battery guide has installed benchmarks to hold a quote against.

If you don’t have panels yet, the inputs are the draw. Four to eight 500 W panels on a wall, a flat garage roof or a frame in the garden can feed the battery directly, with no separate solar inverter. They aren’t plug-in solar, though. They’re part of a fixed installation, so the cabling is part of the electrician’s job as well.

Where the panels can go in England

England’s planning rules for solar changed on 27 August 2026, the same day as the plug-in law. Under the updated permitted development rights, wall-mounted panels can stand out up to 0.2 m from a wall facing a road and 0.4 m from any other wall. On a pitched roof the limit is 0.2 m, and on a flat roof 0.6 m. Free-standing panels in the garden are capped at 9 m², about four 500 W panels’ worth, and at between 1 m and 4 m high depending on how close they sit to the boundary. Listed buildings are excluded, and in conservation areas walls facing a road are off limits. Wales and Scotland set their own rules.

Backup in a power cut

Both batteries keep a backup outlet live when the grid goes down, but only that outlet. Anker says the Solarbank 4 Pro switches its off-grid port on within 10 milliseconds and supplies up to 2,500 W. EcoFlow says the STREAM 5000 switches to off-grid mode immediately and powers its AC outlet at 2,500 W, or 3,000 W with an expansion battery. EcoFlow’s UK page doesn’t give a switchover time.

Everything else in the house goes off, because grid-connected inverters must stop feeding the network in a power cut to protect engineers working on the lines. If you want the fridge, the boiler and a few lights to stay on, ask the electrician to wire a small backup circuit to the off-grid port. A 5 kWh battery will run a fridge-freezer, router and LED lighting for well over a day. My guide to what happens to solar panels in a power cut explains the shutdown, and my DELTA Pro whole-house backup guide covers changeover switches if you want more than a circuit or two.

Apps, tariffs and Octopus

Both apps will charge the battery cheaply overnight and run the house from it at peak times, which is where most of the money is. The details differ.

Anker’s app has smart, custom, dynamic tariff, time-of-use, rapid charging and Storm Guard modes, and Anker says its time-of-use scheduling works with more than 870 suppliers’ tariffs, Octopus included. Without the Smart Meter Gen 2 you only get custom mode, and the battery can’t stop itself exporting.

EcoFlow’s intelligent mode uses weather forecasts plus time-of-use or dynamic prices, and a peak-shaving mode caps how much you draw from the grid. Its Local Mode keeps the battery running without an internet connection if you have a compatible meter, although forecasts and tariff features switch off. EcoFlow says Home Assistant support is planned but isn’t live yet.

One Octopus detail could tip it. Octopus lists EcoFlow among the brands supported by Charge Pack, which guarantees at least £12 a month in account credit, and Anker isn’t on the list. Octopus doesn’t name models, so check the STREAM is covered before you count on it. My Octopus Agile and Flux battery guide has the wider compatibility picture.

Export payments are a separate question. The Smart Export Guarantee, and tariffs such as Outgoing Octopus at 12p/kWh as I write, need proof that a certified installer fitted your solar, usually an MCS certificate. If you want export income, ask before you buy whether your installer will register the panels under MCS. My SEG tariff comparison has the current rates.

The 800 W limit, and why it doesn’t cover either battery

The new law is SI 2026/848, which came into force on 27 August 2026. It lets a plug-in microgenerator connect through an ordinary socket in England, Wales and Scotland, and the definition is tight. The device has to make electricity directly from sunlight, have an AC output of no more than 800 W, connect through a standard plug, run in parallel with the grid, and not be designed to take electricity from your home’s wiring to store for later.

A battery falls at that last hurdle. Storing electricity from your home’s wiring is exactly what it’s designed to do, and both of these charge from the grid on cheap tariffs. The government’s product specification, published on 16 July, also lists plug-in batteries as outside its scope. You can read the decision and the spec on the government’s plug-in solar consultation page, and my breakdown of the DESNZ decision covers what changed between draft and final.

So why does 800 W turn up on both spec sheets? Because both batteries were built for Europe first, and Germany caps plug-in systems at 800 VA. EcoFlow’s UK page says the STREAM’s default output is the regional plug-and-play limit, with 800 W given as the German example. Anker’s UK version ships set to 800 W, and the full 2,500 W is unlocked once an electrician has hardwired it.

Turning the output down doesn’t change anything legally. The battery still stores electricity from your wiring, and the wiring regulations still bar a generating source from connecting to a final circuit with a plug and socket. If you’re buying a plug-in kit for the balcony as well, check it’s a registered kit with my guide to whether your plug-in solar kit is legal.

Why you’d want more than 800 W anyway

Once it’s hardwired, the extra output earns its keep. At 800 W, a full 5 kWh battery takes over six hours to empty, more than twice as long as the 4pm to 7pm peak. At 2,500 W it’s two hours, and at 3,000 W about an hour and 40 minutes. A 3 kW kettle running off an 800 W battery still pulls 2.2 kW from the grid.

Why both still need an electrician

Both companies now say it plainly. Anker’s UK page says the Solarbank 4 Pro must be installed by a Part P-registered electrician on a dedicated hardwired circuit, with a G98 notification to your network operator within 28 days. EcoFlow’s says the STREAM comes with a cable with bare ends and no plug, must be installed by a certified, registered electrician, and mustn’t be connected to a household socket to feed power in.

EcoFlow learned this the hard way. In April 2026 the Advertising Standards Authority upheld a complaint about a STREAM page on EcoFlow’s UK site that promised “Effortless DIY installation – no electrician required”. The ASA said UK rules require the cable to be wired into the distribution board by a certified installer or electrician.

The reason goes deeper than paperwork. A battery feeding a socket circuit adds current the breaker in your consumer unit can’t see, so parts of the cable can end up carrying more than the breaker was chosen to protect. That’s why the wiring regulations bar generating sources from plugging into a final circuit, and why these batteries get a circuit of their own with nothing else on it. I’ve put numbers on that, and covered when true plug-in batteries might arrive, in my guide to plug-in batteries in the UK. The short answer is late 2027 at the very earliest.

What the electrician actually does

1. Picks a spot that meets the battery siting rules, which I cover in the next section.
2. Runs a new circuit from your consumer unit with its own RCBO and an isolator, with nothing else connected to it.
3. Fits the meter clamp on your incoming supply so the battery can follow your usage.
4. Tests everything, issues an Electrical Installation Certificate and notifies Building Control through their competent person scheme. In England and Wales a new circuit is notifiable work under Part P.
5. Notifies your network operator under G98 within 28 days, or applies under G99 before fitting if your total is over 16 A.
6. Wires a backup circuit to the off-grid port, if you want one.

Renting or leasehold? Hardwiring is an alteration, so get written consent from your landlord or freeholder before you buy anything. And use an electrician whose registration you can check; my installer vetting checklist covers what to ask.

The 16 A limit and where the battery can go

G98 is the connection rule for small generators, and batteries count when they export. It covers up to 16 A per phase, about 3.68 kW on a normal single-phase supply, and your installer simply notifies the network operator within 28 days. Go over 16 A in total and it’s G99, which means applying before the installation and waiting for approval.

On their own, both batteries fit comfortably. The trouble starts when there’s other generation in the house.

Add an 800 W plug-in kit and the EcoFlow at full output tips you over, to 16.5 A. If you already have a 3.68 kW rooftop system, either battery takes you well past the limit. Ask your installer how they’ll handle it before you pay a deposit. Some will set the system up to stay inside 16 A, and others will make a G99 application, which can take weeks.

Where the battery can go

Since 15 October 2026, Amendment 4 of BS 7671 has been the only current edition of the wiring regulations, and it has a new chapter on stationary batteries. Together with PAS 63100, the fire-safety specification installers work to, that rules out lofts and roof voids, escape routes such as hallways, landings and stairs, and rooms where people sleep. Garages, utility rooms and outside walls are the usual spots. Both batteries are rated for outdoor use, IP66 on the Anker and IP65 on the EcoFlow, and both run from −20 to 55°C.

PAS 63100 also caps how much battery one home can have: 40 kWh indoors, or 80 kWh outside or in a detached or properly fire-separated garage. Anker’s 30 kWh maximum fits under both. EcoFlow’s headline 90 kWh across six units doesn’t, so treat it as a brochure figure in a UK house. Weight matters too, because a full 30 kWh Anker stack comes to about 260 kg. My home battery fire safety guide has the full siting rules, and if your home is listed, speak to the council before anything gets fixed to its walls.

Savings and payback

Both companies publish savings figures, and both deserve a pinch of salt. Anker’s UK page says up to £770 a year and a payback of about 3.3 years, but that’s for a set-up with four 500 W panels, and it leaves out installation and taxes. EcoFlow’s page for the AC 5000 headlines £568 a year, based on charging at 9p and avoiding 27p.

Here’s my own sum for the battery on its own. I’ve assumed you charge it overnight at 8p/kWh, use that energy instead of paying the October to December 2026 price cap rate of 26.32p/kWh, do one full cycle a day and lose 10% in the round trip. That’s worth about £286 a year from a 5 kWh battery. Electricity carries no VAT from 1 October 2026 to 31 March 2027, and that’s already reflected in the 26.32p.

On those numbers, both pay for themselves within the 10-year warranty, the Anker about a year sooner. Having an installer supply the battery knocks roughly another year off either. Add panels to the solar inputs and the yearly saving climbs, because every unit of your own solar you use is worth the full 26.32p, but so does the bill for panels, mounting and cabling. A second 5 kWh battery only doubles the saving if your home really uses 9 kWh or more a day outside the cheap overnight window.

Which one should you buy?

It depends more on your house than on the batteries. Here’s how I’d call it.

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