Just like the railways, the French army needed reliable, portable energy sources. In the 1930s, Saft worked to supply it with batteries, and even designed one for submarines.
Saft started working for the army in the 1930s, which led the company to supply batteries to the navy for its submarines. During that period, a series of technological breakthroughs enabled Saft to improve its products. As early as 1925, the company was producing batteries with negative cadmium plates, which offered advantages over iron plates in certain uses. In 1928, the Edison patents passed into the public domain: Saft was then able to offer batteries with more efficient tubular positive plates.
Based on this technology, Saft developed a starter battery for the army. After successful tests, this battery was to be used in all combat vehicles. Then, at the beginning of 1934, the company received an order for a large-capacity alkaline nickel-cadmium battery for a submarine. The first tests proved successful. A 480-cell battery was ordered in 1936 for the Ouessant submarine, then under construction.
According to an official test report, the battery was ready when the submarine was commissioned for active service. It was of particular interest to the navy due to its "low hydrogen release, high endurance when diving, and excellent performance in maintaining electrical insulation". In fact, this battery quadrupled the operating autonomy of the Ouessant compared to France's first three submarines. Saft immediately received a new order, this time for the Roland-Morillot submarine. The new battery was delivered to Cherbourg in 1940.
The Ouessant conducted several patrols in the Atlantic, and off the American and Caribbean coasts. In June 1940, during the "phoney war" period, the vessel was moored at Brest for a major refit. In view of the German army's rapid progress, the decision was taken to scuttle the submarine. However, this was the start of a real odyssey for the Ouessant. The German army raised it and towed it to Bordeaux in 1942, for use as an electric power plant. It was scuttled again in Pauillac in 1944. Refloated once again in 1948, it was transformed into a wreck retriever and with the help of another vessel, the Agosta, it was towed to the Gironde in November 1947.
As for the Roland-Morillot, it was destroyed on its building berth when it was three-quarters completed.
The Ouessant stayed in the Bay of Brest, at a depth of 15 meters, until 1942, when it was refloated. The German navy, deeming that the battery was unusable, returned it to Saft.
Despite having spent eighteen months in seawater, all the battery plates were salvageable and were reused in production, which says a lot about the quality and sturdiness of this first battery.
Today, Saft is still working on batteries for the propulsion of submarines, now using lithium-ion technology; these higher-performance batteries are used not only in submarines but also in other civilian and naval vessels.
The Second World War also affected Saft's Romainville factory, which was closed down, then re-opened in September 1940 under the control of a German Commissioner.
Meanwhile, Saft settled in Saint-Cybard near Angoulême, where he opened a new factory in former textile workshops. This new production unit specializing in military batteries employed up to 600 people in the 1960s. It remained in operation until 1984.