Fifty five batteries that neither balancing nor reserve data can see
We map 217 operating batteries in Great Britain by reading two sources: the balancing mechanism, and NESO's response and reserve auctions. Adding a third source showed us 55 more that neither of the first two can see at all.
How they hide
A battery becomes visible in the balancing mechanism when it registers as a balancing unit, and in the reserve data when it wins an auction. A site that does neither is invisible, no matter how large it is. It can still hold a capacity market agreement, because that is a separate contract with a separate register.
So we read the capacity market register, priced every live battery agreement at the auction that awarded it, and tried to attach each one to a site we already had on the map. Fifty five would not attach to anything within five kilometres.
What they are worth
The largest is Gateway Energy Centre at 127 megawatts de-rated, which on a two hour battery implies something in the region of three hundred megawatts of connected power. That is a top ten asset by size and it appears nowhere in the data most people use.
Why this matters more than the number
Every published figure about the Great Britain battery fleet, including ours, is built from a source that has a blind spot. An index built only from balancing units excludes every battery that does not register as one. A count built from reserve auctions excludes everyone who did not bid. Nobody states the size of what they are missing, because to state it you need a fourth source to measure it against.
This is our attempt to state ours. Our fleet is 217 sites and 7,194 megawatts. The capacity market says there are at least 55 more sites out there, and it can only see the ones that hold an agreement, so the true number is higher again.
What we cannot tell you about them
Almost everything. We have a name, a holder, a de-rated capacity and a coordinate. No earnings, because they earn in markets that do not publish per site. No live position, because they do not notify one. No duration for most of them. They are a headcount and an outline, and that is all the published data supports.
They are not on the map for that reason. Putting a dot on a map for something we know nothing about would imply a confidence we do not have.
Capacity market register read on 22 August 2026, priced at the clearing price of each awarding auction. Method and its defects are on the capacity market method page.