Black Friday Battery Deals: How to Judge a Discount by the Usable kWh
- Black Friday falls on 27 November this year, and battery sellers began their campaigns in the middle of the month.
- A percentage discount depends on the starting price, which you cannot always check.
- Compare the price divided by usable kWh, not by the nominal capacity on the box.
- Check what is included: inverter, installation, accessories and warranty terms.
- The numbers in the worked example are illustrative, not real prices.
Black Friday battery campaigns are already running, some promising up to 60% off. A big percentage tells you little. The number that lets you compare two batteries is the price per kilowatt-hour you can actually use.
Why the headline percentage misleads
A sale of "up to 60% off" is a ceiling for the best-discounted item, not a typical saving. On 12 November, for example, the maker WattCycle announced a Black Friday sale of up to 60% off across its website. The wording says nothing about which products get the deepest cut or what the earlier price was.
A comparison with a "was" price is only useful if that price was genuine. UK Competition and Markets Authority guidance, written for online mattress sellers, says a price comparison must reflect a genuine price advantage. A High Court ruling later rejected the regulator's proposed fixed sales ratio, so the test is not a simple formula. In practice, a screenshot of the same price a month ago tells you more than the strikethrough does.
Work out the price per usable kWh
Divide the price by the energy you can really draw out. Nominal capacity is the figure on the label. Usable capacity is lower, because batteries keep a reserve to protect the cells. Our guide to kW and kWh explains the two units.
Here is an illustrative example with made-up prices. Unit A has 5 kWh nominal and 90% usable, so 4.5 kWh, and costs £1,350: that is £300 per usable kWh. Unit B has 6 kWh nominal and 80% usable, so 4.8 kWh, and costs £1,200: that is £250 per usable kWh. The cheaper unit with the bigger label is also the better value, but only the division shows it.
Good to know
We have not listed prices for any product. Sale prices change daily, so check the seller's page on the day you buy.
Check what the price includes
A battery price may or may not include the inverter, the control unit, cables, mounting and fitting. A power station is a complete box, while many home batteries are sold as a module that still needs an inverter and an installer. Add those costs before you divide.
- Is the inverter or hybrid inverter included, and is it compatible with your solar system?
- Does the quote include installation, commissioning and the grid notification?
- What are the warranty years, the cycle limit and the minimum capacity it promises at the end?
- Is the price the same for the UK, or is it a model sold elsewhere?
Slow down on the pressure tactics
Countdown clocks and "only a few left" messages are designed to speed up your decision. A battery that will sit in your home for ten years or more is worth a day of checking. Our guide to sales pitches and red flags lists what to ask before you sign, and the UK cost guide gives context on what batteries tend to cost.
Common questions
Are Black Friday battery deals real discounts?
Some are and some are not. Look for the price history, compare several sellers, and divide by usable kWh. A deep discount on an overpriced item can still cost more than a shallow one on a fairly priced unit.
Is it worth waiting for a sale?
Only if you do not need the battery now. Each week without a battery means missing the savings it would make, and an inflated price can wipe out a discount. Decide based on your own electricity use, not the calendar.
Does the sale change my warranty?
It should not, but check. Look at the warranty terms on the exact product page you buy from, because warranty length can differ between sellers and regions. Our warranty checklist shows what to look for.
Sources
- WattCycle: Black Friday sale announcement (GlobeNewswire, 12 November 2026)
- GOV.UK: Discount and reference pricing principles for selling mattresses online (CMA)
Related guides
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