On September 24, Mercedes-Benz AG and ProLogium Holding signed a joint testing agreement giving the German carmaker priority access to ProLogium’s Gen 4 cells — the latest move in a Mercedes solid-state battery programme that is now running on two tracks. Three weeks earlier, a lightly modified Mercedes EQS covered 1,205 km from Stuttgart to Malmö on a single charge using lithium-metal solid-state cells from Factorial Energy. What Mercedes-Benz signed in September is not that. It is a testing agreement, and it carries no order, no vehicle and no date.
Mercedes Solid-State Battery Deal: What Was Actually Signed
The agreement gives Mercedes-Benz priority access to ProLogium’s Gen 4 cells for a preliminary technology evaluation. The cells will go through electrical, thermal and safety testing at Mercedes-Benz’s own facilities and at specialised external institutes, and the results will be used to assess the technology’s “suitability for potential use in future vehicles” — ProLogium’s phrasing in its announcement of the agreement.
That is the whole of it. Neither company announced a production vehicle, a commercial order, an annual volume or a launch date, and no testing schedule or vehicle programme was named. The context makes the modesty notable: the two companies have worked together since 2016, Mercedes-Benz is a strategic investor in ProLogium, and it holds a seat on the board of directors. Over that period the collaboration has validated pouch cells, a first-generation prismatic cell and ProLogium’s bi-polar architecture. Mercedes-Benz has announced no production vehicle using any of them.
What Gen 4 is, in ProLogium’s description, is a “Superfluidized All Inorganic” lithium ceramic battery: a non-flammable inorganic electrolyte, a ceramic separator and a proprietary active safety mechanism, packaged against five targets at once — intrinsic safety, high performance, high energy density, scalable manufacturing and a competitive cost structure. Both executives framed the agreement as a step in a sequence rather than a destination. ProLogium founder and chief executive Vincent Yang called the test “testing our latest Gen 4 technology for future vehicle applications”, while Mercedes-Benz board member Jörg Burzer described it as “the next step in exploring advanced battery technologies for future electric vehicles”.
Gen 3.5 Is in Production. Gen 4 Is on a Test Bench.
On September 2, ProLogium said its Gen 3.5 Lithium Ceramic Battery had entered mass production at its Taoke gigafactory in Taoyuan, Taiwan, China. The supporting evidence came from third parties rather than the company’s own bench: TÜV tested a large-format 185.4 Ah cell at 381 Wh/kg gravimetric and 903 Wh/L volumetric energy density, and UL Solutions, applying China’s GB/T 43568-2026 methodology, recorded mass loss below 0.05% after six hours under vacuum at 120°C — under the 0.5% ceiling the standard sets for an all-solid-state classification. That release is published in full on ProLogium’s newsroom.
Gen 3.5 is built on ProLogium’s Logithium cell architecture, which pairs a ceramic separator with a proprietary edge-frame structure around the electrode perimeter. Gen 4 moves to a fully inorganic electrolyte system — which means the cell Mercedes-Benz has secured priority access to test is not the cell ProLogium has just put into production. The rollout is a ladder, not a switch.
| Generation | What ProLogium says about it | Status |
|---|---|---|
| Gen 3 (early hybrid solid-state) | “More than 10 years of commercial references across industries” | In commercial use |
| Gen 3.5 (lithium ceramic, Logithium architecture) | TÜV: 185.4 Ah, 381 Wh/kg, 903 Wh/L. UL Solutions: all-solid-state under GB/T 43568-2026 | Mass production at Taoke since September 2026 |
| Gen 4 (Superfluidized, all-inorganic) | Non-flammable inorganic electrolyte, ceramic separator, active safety mechanism | Under evaluation by Mercedes-Benz; agreement signed 24 September 2026 |
What “Mass Production” Means on a 0.5 GWh Line
ProLogium describes Taoke as a Giga-level facility. Its initial operating capacity is 0.5 GWh, with expansion toward 1–2 GWh planned, as CarNewsChina reported when it read the September 2 announcement in full. Half a gigawatt-hour is a production programme, not a supply chain. At 0.5 GWh a year and an 80 kWh pack, the theoretical output is around 6,250 packs — enough to validate a chemistry and prove a line, not enough to feed a vehicle programme.
ProLogium’s cumulative shipment figure needs the same treatment. Since commercial production began in 2013 the company has shipped more than 2.4 million cells on the lithium ceramic platform, and its disclosed automotive business — supply to a US automotive audio-system company whose parts go into vehicles from a Japanese automaker sold in North America — accounts for over 900,000 of them across more than 175 repeat orders. Those are production evidence. They are not traction cells, and ProLogium separately reports roughly 10,000 automotive battery samples, which is the number that describes its position in the car business.
European volume is supposed to come from Dunkirk. ProLogium broke ground on the first phase in February 2026; that phase is designed for 4.0 GWh a year, expected to be progressively achieved by 2030, against a site maximum of 44 GWh. And Dunkirk is scoped for the generation still on the test bench: Batteries International reported that the French plant is intended to build ProLogium’s “fourth generation superfluidised all-inorganic solid-state lithium ceramic battery”.
| Facility | Designed capacity | Timing |
|---|---|---|
| Taoke, Taoyuan (operating) | 0.5 GWh initially, toward 1–2 GWh | Operating since 2024 |
| Dunkirk, France — phase 1 | 4.0 GWh a year | “Progressive”, by 2030 |
| Dunkirk, France — full site | Up to 44.0 GWh | Not scheduled |
Mercedes-Benz Already Has a Solid-State Battery on the Road
The comparison that matters most sits inside the Mercedes solid-state battery effort itself. At the end of August 2026, a lightly modified EQS test vehicle drove 1,205 km from Stuttgart to Malmö, Sweden, without a single charging stop and arrived with 137 km of range remaining. The cells were lithium-metal solid-state units from Factorial Energy, built on the company’s FEST chemistry and packaged with Mercedes-AMG High Performance Powertrains in Brixworth, United Kingdom. The pack holds roughly 25% more usable energy than a standard EQS battery at comparable weight and volume, with pneumatic actuators managing the cell volume changes the chemistry produces — all of it described in Mercedes-Benz’s own press information on the run.
Mercedes-Benz announced the start of public-road testing in February and describes the Malmö drive as part of a validation programme that also covers simulation and bench testing at Stuttgart-Untertürkheim and Sindelfingen. Its stated goal is series production of solid-state technology by the end of the decade. ProLogium’s Gen 4 is therefore not Mercedes-Benz’s only solid-state option. It is the second one, and it is the one still in the laboratory queue.
“Superfluidized” Is Not the Same as Fully Solid
The word in the product name is doing work. ProLogium describes Gen 4 as a Superfluidized Inorganic battery — a formulation the company says integrates “the respective advantages of solid-state and liquid battery technologies”, positioned on manufacturability and cost rather than on purity of concept. The “all inorganic” label refers to the electrolyte system: a non-flammable inorganic electrolyte plus a ceramic separator.
That distinction matters because “solid-state” is a term under active policing. China’s GB/T 43568-2026, in force since July 2026, sets a measurable boundary — no more than 0.5% mass loss after six hours under vacuum at 120°C — and the standard has been submitted to the IEC as a reference for international work. ProLogium’s Gen 3.5 cell came in under 0.05%, which is how it claims all-solid-state status under that method. Calling Gen 4 “all inorganic” rather than “all solid” is the vocabulary of a company that knows exactly where the line is drawn.
The competing route is worth keeping in view. Factorial — the company whose cells are already in that EQS — builds on a quasi-solid polymer electrolyte and has been expanding into sulfide chemistry through its Mitsui Kinzoku partnership. Ceramic and sulfide systems carry different interface, processing and cost trade-offs, and Mercedes-Benz is currently funding test work on both.
The Listing Underneath the Testing Agreement
The agreement carries a second function. ProLogium’s announcement states that Mercedes-Benz “is fully supportive of ProLogium’s development plans for its Dunkirk plant as well as ProLogium’s further plans to become publicly listed on the NASDAQ in 4Q2026”. ProLogium agreed a business combination with Translational Development Acquisition Corp (Nasdaq: TDAC) in May 2026, has filed a registration statement on Form F-4 with the US Securities and Exchange Commission, and expects to list under the ticker PRLG.
Read the sequence as an investor would. A decade-long shareholder and board member attaches its name to a testing agreement in September, and the company’s own release uses the same paragraph to restate a fourth-quarter listing. For a business whose commercial volume is still measured in audio-system cells and automotive samples, an automaker willing to test in public is part of the equity story — as is the other September news that Kyushu Electric Power, an existing partner, confirmed a strategic investment in the company.
The Bottom Line: Mercedes-Benz has priority access to test ProLogium’s Gen 4 solid-state cells under a joint agreement signed on September 24 — with no order, no vehicle, no volume and no schedule disclosed. The generation ProLogium has actually put into mass production is Gen 3.5, on a Taoyuan line whose initial capacity is 0.5 GWh, while the French factory scoped for Gen 4 targets 4.0 GWh by 2030. And Mercedes-Benz already has a solid-state battery on the road. It just is not this one.
Accuracy note: The terms of the agreement — priority access, electrical, thermal and safety testing at Mercedes-Benz facilities and external institutes, and the “suitability for potential use in future vehicles” framing — are as stated in ProLogium’s press release of September 24, 2026. Neither company disclosed a testing schedule, a vehicle programme, an order, a volume or a price. The Gen 3.5 figures of 381 Wh/kg and 903 Wh/L come from a TÜV test report that ProLogium cites but has not published, and the UL Solutions result under GB/T 43568-2026 is likewise reported by ProLogium; both are third-party tests as described by the company, and we have not seen the underlying reports. The 0.5 GWh initial capacity and the 1–2 GWh expansion plan are from CarNewsChina’s reporting of the September 2 announcement, not from a ProLogium figure, and the 6,250-pack calculation is our own arithmetic on an 80 kWh pack assumption. The EQS figures — 1,205 km, 137 km remaining, 25% more usable energy — are Mercedes-Benz’s own, describe a purpose-built test vehicle with pneumatic actuators, and are not a production-pack specification. Dunkirk capacity and timing are ProLogium’s own; “progressively achieved by 2030” is the company’s phrasing and is not a committed date. No production cost for Gen 3.5 or Gen 4 has been disclosed by anyone, so no cost comparison is made here. The observation that Gen 3.5 is the generation in production while Gen 4 is the generation under evaluation is drawn from ProLogium’s releases of September 2 and September 24.
Sourcing note: ProLogium’s press releases of September 2 and September 24, 2026 are the primary sources for the agreement, the generation ladder, the cell specifications and the listing plans. Mercedes-Benz’s own press information on the EQS solid-state long-distance test is the source for the Factorial programme, the 1,205 km figure, the pneumatic actuators and the energy-density gain. CarNewsChina (September 6) supplied the production-capacity context and the distinction between cells shipped and traction cells; Batteries International (February 2026 and September 2026) supplied Dunkirk’s fourth-generation scope and the Kyushu Electric Power investment. EVsays did not attend any ProLogium or Mercedes-Benz event, has not tested any product, and has received no information from either company beyond its public materials. See our editorial policy and correction policy.
Sources & Further Reading
- ProLogium Technology — “Mercedes-Benz and ProLogium have entered into a joint testing agreement, including a preliminary technology evaluation of ProLogium’s latest Gen4 Superfluidized All Inorganic Solid State Battery Cell Technology” (2026-09-24) — the primary source for the agreement, the testing scope, the Gen 4 architecture, the partnership history and the Nasdaq plans.
- ProLogium Technology — “ProLogium Begins Mass Production of High-Energy-Density All-Solid-State Battery, Reaching 381 Wh/kg and 903 Wh/L” (2026-09-02) — the Gen 3.5 mass-production claim, the TÜV and UL Solutions test results, the Logithium architecture, the manufacturing generations and the cumulative shipment and automotive-order figures.
- Mercedes-Benz — “Long-distance test successfully completed: EQS with solid-state battery covers 1,205 km on a single charge” (press information) — the Stuttgart–Malmö drive, the Factorial Energy cells and FEST chemistry, the Mercedes-AMG High Performance Powertrains packaging, the pneumatic actuators and the stated series-production ambition.
- CarNewsChina — “Mercedes-backed ProLogium starts 381 Wh/kg solid-state production as carmakers watch from sidelines” (2026-09-06) — the 0.5 GWh initial capacity and 1–2 GWh expansion plan, the pack-equivalent arithmetic, and the distinction between cumulative cell shipments and traction cells.
- Batteries International — “ProLogium investment boost as Taiwan Li ceramic plant ramps up” — Dunkirk’s scope as the European plant for the fourth-generation superfluidised all-inorganic cell, the Kyushu Electric Power investment, and the energy-density comparison table.
- EVsays — the earlier threads this sits on: ProLogium’s entry into production, the solid-state race to 2027, the sulfide electrolyte bottleneck and the Chinese solid-state standard now before the IEC.
