Electric ships are a modest business. Most estimates put the global market at under US $5 billion in 2025. But the business is growing, and it is drawing more battery makers. The latest is Xing Mobility, of Taoyuan City, Taiwan. In September, at the SMM Hamburg maritime trade fair, it unveiled its Immersio CTP pack. The pack submerges every cell in a fluid that absorbs heat without conducting electricity but is, notably, flammable.

Xing is not the first to pursue that idea. Kreisel Electric, of Rainbach im Mühlkreis, Austria, won certification for an immersion-cooled marine battery pack in 2023. Its batteries are now powering the P-12 hydrofoil ferry built by Candela, of Stockholm. Wattalps, of Moirans, France, received an approval for its marine batteries in January 2026 from Bureau Veritas, of Neuilly-sur-Seine, France. Xing’s pitch is density. The company says its CTP stores up to twice the energy of conventional marine batteries. It also says its immersion scheme keeps one overheating cell from igniting the rest.

Those claims rest mostly on laboratory data. Only two vessels run on Xing packs, and neither uses the CTP. And the pack has yet to gain approval from DNV, a ship-equipment certifier in Høvik, Norway. Meanwhile, European Union emissions rules are pushing shipowners toward battery power. That pressure makes Xing’s claims worth examining, starting with the one about energy doubling.

Does the Xing CTP Battery Really Double Energy Density?

Most packs hold cells in metal module boxes inside a larger enclosure. The CTP, short for cell-to-pack, omits both layers. A molded composite holder grips the cells, channels the coolant, and forms the structure. “Everything is integrated into one piece,” says Royce Hong, Xing’s founder and CEO. Less structure means less dead weight for each kilowatt-hour stored.

Cedric Lin, senior engineering manager at Xing, says the CTP stores about 200 watt-hours per kilogram in lab tests. He says that pack-level figure includes the coolant and battery-management system. The CTP uses cylindrical 21700 cells, mainly nickel manganese cobalt or nickel cobalt aluminum. Both store more energy per kilogram than the lithium iron phosphate (LFP) packs that Xing used for comparison in its calculations for making its doubling claim.

A more competitive metric is presented by the market leader: Corvus Energy, of Bergen, Norway, which has supplied more than 1,300 maritime projects. Corvus Energy’s data sheets list 168 Wh/kg for its Dolphin NxtGen Energy system. Xing’s CTP beats that, but by only 19 percent (and only according to measurements made in a lab).

Xing Mobility’s batteries are being used in the Porrima P111, the largest solar-powered catamaran in the world.Porrima

The harder test is power. Ships draw heavily, sometimes draining a battery in as little as 20 minutes. Fast discharge, like fast charging, generates a lot of heat. Whether lab results hold at sea depends on how the CTP sheds that heat, and on what happens when a cell fails.

Immersion Cooling Versus Cold Plates

Most marine batteries shed heat through cold plates, metal plates with tiny channels that carry coolant past the cells. But heat must first cross the cell casing, thermal paste, and plate wall. Each layer slows the transfer. Submerging every cell removes those layers. Paul A. Kohl, a chemical and biomolecular engineering professor at Georgia Tech, in Atlanta, backs that reasoning. “Liquid immersion is about as good as heat transfer gets,” he says.

That advantage matters most in thermal runaway, when one damaged cell overheats and ignites its neighbors. Xing’s documentation says immersion can cool a punctured cell from about 1,000 °C to below 100 °C within 10 seconds. Kohl finds that plausible: “It’s well within the realm of feasibility,” he says.

Plausible is not proved, though. Lin says Xing has tested the CTP many times to IEC 62619, an international safety standard for industrial lithium batteries. Those tests ran in laboratories certified by the testing firms TÜV and Intertek, and they tracked cell temperatures over time. Lin did not share the results, nor did he say whether the testers confirmed the 10-second figure.

The tests also leave open a question about the oil itself. Kohl says most immersion systems he has seen use fluorocarbons or silicones, which resist burning. Wattalps, for example, uses a nonflammable fluid. Xing’s nickel-rich cells raise the stakes, because they enter thermal runaway more readily than LFP cells. A failing cell can generate sparks and release oxygen, Kohl explains, and a pack holds a lot of oil. “Using a flammable liquid, of course, you’re throwing away part of the advantage of the immersion battery,” he says.

Longevity is a second question. Lin says the oil lasts as long as the battery, because packs run near room temperature. Kohl is less sure. Over a decade, the fluid heats and cools thousands of times, and oils slowly break down. At sea, water and salt can also contaminate it. “Ten years’ reliability and no degradation is a very demanding requirement,” Kohl says.

What Matters in a Hull Is Space, Not Weight

Xing also touts the compact nature of its CTP system. Aboard a ship, battery volume matters more than mass. Every cubic meter filled by a battery fill is one lost to cargo or passengers. Lin says the packs that Xing now mass-produces store 330 to 350 watt-hours per liter. For comparison, Corvus lists 212.5 Wh/L for its Dolphin NxtGen Energy system.

Xing credits the design. Because the CTP needs no cold plates, cooling pipes, or module boxes, its cells can be packed more tightly. The company also argues that immersion contains failures well enough to place cells and whole packs closer than usual. Kohl says tighter packing makes the doubling claim feasible—if the fluid reliably stops fire from spreading.

Xing has submitted the CTP design to DNV for document review and has begun preparing for physical tests. Hong says DNV approval matters most on large passenger ferries, where many lives are at stake. Smaller vessels and some cargo ships can install the CTP sooner, he says. So, the pack’s first voyages will likely come on small boats carrying few people. Those trips will finally expose Xing’s numbers to salt air, constant vibration, and months of heat cycles. Until then, Kohl’s verdict on the cooling claim fits the whole pitch: plausible, but not yet proved.