France's biggest battery published its first report card - 145 full cycles in 125 days and 70.5 GWh fed back from a 240 MW / 480 MWh site
TagEnergy and Banque des Territoires inaugurated the Cernay-les-Reims battery on 1 October. It is 240 MW / 480 MWh, in commercial operation since May 2026, and the owners say it has already fed 70.5 GWh back into the grid across 145 full cycles in 125 days. Revenue is not published.
Most big battery news is a promise. This one came with a report card.
TagEnergy and Banque des Territoires inaugurated their battery at Cernay-les-Reims, near Reims in France, on 1 October 2026. The site is 240 MW / 480 MWh. That is two hours at full power (480 divided by 240). It has run commercially since May 2026 and the owners call it the largest operating battery in France.
The numbers they published, as at 23 September: 70.5 GWh fed back into the grid, and 145 full charge-and-discharge cycles in 125 days. That is a bit more than one full cycle a day.
First, the terms. MW is how hard the battery can push. MWh is how much it holds. Think of MW as the width of the tap and MWh as the size of the tank. One "cycle" means filling the tank and emptying it once.
Analogy: it is like a delivery van that does just over one full run a day, every day, all winter and summer. A van parked in the yard earns nothing. This one is out on the road.
The build: 140 Tesla Megapack containers on just over 3 hectares, wired into the national grid at 225 kV. Tesla supplied the kit and runs the market interface. Eiffage did civil and electrical works. It sells fast grid services (frequency and voltage support) as well as shifting energy. Banque des Territoires owns 49%.
Workplace meaning. A grid battery cycling more than once a day tells you the market is paying to soak up cheap midday power and give it back later. That is the same daily move a factory or cold store battery makes behind the meter: charge on cheap solar, discharge into the expensive evening hours. The difference is scale and who gets paid.
Good: Real operating data, not a forecast. Energy fed back, cycle count and days in service all line up (145 cycles x 480 MWh is about 70 GWh).
Bad: No revenue, no price per MWh, no split between grid services and energy trading. You cannot work out what one cycle earned.
Ugly: Cycling hard wears cells faster. The release does not say what warranty cycle budget this site runs on, or how degradation is tracking. Four months is a good start, not a lifetime.
Soft next step: when you size a site battery, ask the supplier how many cycles a year the warranty covers and how hard your tariff will make it work. Then a short consult at Sovryn Energy /consult if you want that checked against your bills.
Source: TagEnergy and Banque des Territoires press release, Cernay-les-Reims, 1 Oct 2026 - inauguration of France's largest battery storage installation. Primary for 240 MW / 480 MWh, commercial operation since May 2026, 70.5 GWh fed back and 145 full cycles in 125 days (as at 23 Sep 2026), 41,635 work hours, 140 Tesla Megapacks on ~3 ha, 225 kV RTE connection, FCR/aFRR and voltage services, Tesla / Eiffage roles, Banque des Territoires 49%. Follow-up: pv magazine Global, 7 Oct 2026, https://www.pv-magazine.com/2026/10/07/frances-largest-battery-goes-online/