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Written and fact-checked by Jacob Whitmore · Published 15 Sep 2026 · How we work

10 of 20 home batteries put a bigger number in the name than you can use

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The short answer

We read the maker datasheets for 20 home battery product lines sold in the UK on 15 September 2026. In 10, the number in the product name is higher than the usable energy the same maker prints, in at least one size. Three print no usable figure at all. The name-to-usable gap ran from 1.4% to 10.2%. Only 2 of the 20 lines publish how much capacity is guaranteed at the end of the warranty.

Checked 15 September 2026 · desk research by Jacob Whitmore. We do not test batteries. Every figure here comes from the maker’s own product page, datasheet, install manual or warranty. This is a claims audit: no product is ranked, there are no affiliate links, and nobody paid to appear.

Who this is for: anyone comparing battery quotes, or adding a battery to solar panels. Who it is not for: anyone choosing an installer. This page rates no firms.

We read 20 product lines on 15 September 2026

  • 20 product lines from 13 makers: Tesla, GivEnergy, SolarEdge, Fox ESS, Huawei, Enphase, myenergi, Duracell Energy, Sigenergy, AlphaESS, Pylontech, Sunsynk and Growatt.
  • 10 carry a number in the name that is higher than the usable energy in their own datasheet, in at least one size.
  • 7 have a name that matches the usable figure.
  • 3 print no usable figure at all.
  • 7 of the 17 lines that print a usable figure also say what temperature and charge rate it was measured at. 10 do not.
  • 2 of 20 publish the capacity guaranteed at the end of the warranty.
  • One maker labels one figure three ways. Tesla’s 13.5 kWh is “Usable Battery Energy” in the Powerwall 3 datasheet, “Nominal Battery Energy” in its UK install manual, and “rated capacity” in its warranty.

Method in six lines

  1. We chose the battery lines most often named by UK installers and suppliers, and opened each maker’s own pages and documents on 15 September 2026.
  2. The name figure is the number in the product or model name, or at the top of the maker’s page. We count a number in a model code (EP11, US5000) because retailers repeat it as kWh.
  3. The usable figure is the maker’s printed usable (or “useable”) energy.
  4. Where a maker’s datasheet was only readable on a distributor’s site, the source list says so.
  5. The name-to-usable gap is our arithmetic: (name figure minus usable) ÷ name figure.
  6. We also read 10 installer, retailer and supplier listings to see which figure they repeat.

The table

20 UK home battery product lines, maker documents read 15 September 2026. DoD = depth of discharge.
Maker, product lineWhere the number appearsName figureTotal or nominal (datasheet)Usable (datasheet)Name-to-usable gapTest conditions printed for usable?End-of-warranty capacity printed?
Duracell Energy Dura5Product name (“5.12KWh”)5.12 kWh5.12 kWh4.6 kWh10.2%NoNo (10 years; 35 MWh throughput printed)
myenergi libbiSystem name (“5kWh System”)5 kWh5.12 kWh4.6 kWh (90% DoD)8.0%NoNo (10 years)
Sunsynk L5.1Model name5.15.12 kWh4.61 kWh (90% DoD)9.6%Yes: 90% DoD, 0.5C, 25°CNo
Growatt ARK XHModel names (ARK5.1XH to ARK17.9XH)5.1 to 17.95.12 to 17.92 kWh4.6 to 16.12 kWh9.8% to 9.9%NoNo (10 years)
Pylontech US5000Model name50004,800 Wh4,560 Wh8.8%NoNo
Fox ESS EP11Model name1110.36 kWh10.36 kWh (100% DoD)5.8%NoNot in datasheet
SolarEdge Home Battery 400VPart number (BAT-10K1P)10Not printed9.7 kWh (100% DoD)3.0%No (depth of discharge only)Not in datasheet (10 years)
Sigenergy SigenStor BAT 6.0Model name6.06.02 kWh5.84 kWh2.7%Yes: 100% DoD, 0.2C, 25°C, beginning of lifeNo
Huawei LUNA2000-5/7/10-S1Model name5 / 7 / 107 size: 6.9 kWh module5 / 6.9 / 10 kWh1.4% (7 size only)Yes: 100% DoD, 0.2C, 25°C, beginning of lifeNo (15 years)
Sigenergy SigenStor BAT 5.0 / 8.0Product header (“kWh”)5.0 / 8.05.38 / 8.06 kWh5.2 / 7.8 kWh-4.0% / 2.5% (the 5.0 size is under-named)Yes: 100% DoD, 0.2C, 25°C, beginning of lifeNo
Tesla Powerwall 3Datasheet and supplier listings13.5 kWhNot separate13.5 kWh (AC)0%Yes: 25°C, 5 kW, beginning of life (UK install manual: 3.3 kW)Yes: 80% at 10 years (UK)
Tesla Powerwall 2 AC (legacy)Datasheet13.5 kWhNot printed13.5 kWh0%Yes: 25°C, 3.3 kWYes: 80% at 10 years (UK)
GivEnergy All in OneProduct name13.5 kWh“Capacity 13.5 kWh”13.5 kWh (100% DoD)0%NoNo (12 years)
GivEnergy Giv-Bat 9.5 Gen 3Product name9.5 kWhNot printed (184 Ah and 51.2 V printed)9.5 kWh0%NoNo (page says both 10 and 12 years)
SolarEdge Home Battery 48VProduct name4.6 kWhNot printed4.6 kWh (4.85 kWh on some new installs)0%No (depth of discharge only)No (10 years)
Huawei LUNA2000-5/10/15-S0Model name5 / 10 / 155 kWh per module5 / 10 / 15 kWh0%Yes: 100% DoD, 0.2C, 25°C, beginning of lifeNot in document
Enphase IQ Battery 5PModel name5Not printed5.0 kWh0%NoYes: more than 60%, up to 15 years or 6,000 cycles
GivEnergy Giv-Bat 5.12 Gen 3Product name5.12 kWh5.12 kWhNot printedn/an/aNo (10 years)
GivEnergy High Voltage StackableProduct name10.2 to 20.4 kWh10.2 to 20.4 kWhNot printed (100% DoD stated)n/an/aNo (12 years)
AlphaESS SMILE-G3-BAT-9.6S / 4.8SModel name9.6 / 4.89.6 / 4.8 kWh (“rated”)Not printed (95% DoD stated)n/an/aNo (10 years)

A note on the second Sigenergy size. The same Sigenergy datasheet as the 6.0 lists a second size at 9.04 kWh total and 8.76 kWh usable. We could not confirm the name printed above that column, so it is left out of the gap range.

What the gap is worth

A kWh of usable capacity that is not there is a kWh you do not shift each day. Cycled once a day, 1 kWh is 365 kWh a year. At the 26.32p October 2026 cap rate that is up to £96.07 a year of grid electricity you would still buy. That is a ceiling: it ignores what you paid to charge the battery, which is why the real value depends on your tariff. On a 5.12 kWh battery with 4.6 kWh usable, the 0.52 kWh gap is worth up to £49.96 a year on the same basis.

Three things the datasheets do not agree on

  1. What usable is measured at. Huawei and Sigenergy measure at 25°C and a gentle 0.2C charge rate, at the start of the battery’s life. Sunsynk uses 0.5C. Tesla quotes 5 kW in one document and 3.3 kW in another. Ten lines do not say. A garage in January is not 25°C.
  2. What is left by year ten. Only Tesla (80% at 10 years, UK) and Enphase (more than 60%, up to 15 years or 6,000 cycles) print a retained-capacity promise. For the other 18 lines, the warranty length tells you how long the battery is covered, not how much of it you can still use.
  3. Warranty length on one page. GivEnergy’s Giv-Bat 9.5 Gen 3 page says “12-year warranty” in its overview and “10 Years” in its specification table.

What installers and suppliers repeat

We read 10 listings. Five label the figure as usable. One (Plug In Solar’s libbi listing) prints both nominal and usable, but its title uses a third figure, “5kWh”. Four give a capacity with no label: Octopus, British Gas, EDF and Segen’s Fox EP11 listing. Segen’s Fox listing also says 90% depth of discharge, where Fox’s own datasheet says 100%.

What to ask before you sign

  • What is the usable kWh, and where is it in the maker’s datasheet?
  • At what temperature and charge rate was it measured?
  • What capacity is guaranteed at the end of the warranty, and is there a throughput cap?
  • Does the warranty need the battery to stay online? Tesla’s full 10 years does.
  • Red flag: a quote that gives one kWh figure and no datasheet.

For sizing a battery, see our solar battery storage guide. For what a battery adds to a solar system’s payback, see our solar panel costs guide and the solar payback index.

What would change these numbers

  • New datasheet versions. Several sheets carry no date, and AlphaESS’s current UK sheet no longer prints the usable figure its older 3.8S sheet did.
  • New product lines, which we will add on the next read.
  • A maker publishing retained-capacity figures.

FAQ

What is the difference between usable and total battery capacity?

Total, or nominal, capacity is everything the cells hold. Usable capacity is what the system lets you draw. Makers hold the difference back to protect the cells.

Is a 5kWh battery really 5kWh?

Not always. Of the lines we read on 15 September 2026, myenergi’s libbi 5kWh system prints 4.6 kWh usable, and Duracell Energy’s 5.12 kWh Dura5 prints 4.6 kWh usable.

Which home batteries publish their end-of-warranty capacity?

Of the 20 product lines we read, only two: Tesla Powerwall (80% at 10 years in the UK, in the warranty document) and Enphase IQ Battery 5P (more than 60%, up to 15 years or 6,000 cycles).

Does a home battery lose capacity in the cold?

Most datasheets we read do not say. Where test conditions are printed they are at 25°C, and Growatt notes that performance is limited below 10°C.

What should I ask an installer about battery capacity?

Ask for the usable kWh and where it appears in the maker’s datasheet, the temperature and charge rate it was measured at, and the capacity guaranteed at the end of the warranty.

Does this page recommend a battery?

No. It is a claims audit. It carries no affiliate links, ranks nothing, and nobody paid to appear.

This page is not financial advice. Check current datasheets and quotes before you buy.

Sources

All read 15 September 2026. Where a maker document was read on a third-party site, the host is named.

JW
Jacob Whitmore
Writer and editor
Jacob Whitmore writes the guides on this site. Most of the work is desk research: published specifications, price tracking and running-cost arithmetic at the current Ofgem rates. Where a product has been bought and used, the guide says so. Where a figure comes from someone else, they are named and linked. Guides carry a date and are revisited when prices or models change.
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Sources & Editorial Standards

Written by Jacob Whitmore under our editorial policy: we do not accept free products in exchange for reviews, and no brand pays to appear or to rank higher. Where this article uses a number we did not measure ourselves, the source is named in the text.

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