General brochure for our high-performances Li-ion batteries with patented immersion cooling technology.

WATTALPS brochure

At WATTALPS, we support shipyards and naval engineers in successfully designing and electrifying their boats by providing advanced battery solutions. 
With 8 patents, WATTALPS batteries are based on Immersion Cooling Technology, delivering best thermalization, performance and safety. Their modular design ensures seamless integration within your space requirements. 
WATTALPS batteries successfully passed the non-propagation of thermal runaway tests witnessed by BV for Maritime Type Approval.

WATTALPS

Safety and Security AWARD-Euromaritime2026

A panel of maritime experts evaluated nearly forty candidates, and awarded five prizes, with WATTALPS winning the one dedicated to safety and security at sea.
The distinction, which recognizes recent progress in maritime battery safety, highlights WATTALPS’ innovative and safe battery solutions for the maritime sector.

WATTALPS Marine Type Approval

Safety at the heart of the qualification process:
To obtain Bureau Veritas Marine Type Approval, WATTALPS batteries successfully passed an extensive series of tests required by the standard, including:

- Electromagnetic Compatibility (EMC) testing, ensuring the batteries operate safely alongside other onboard electronic systems.
- Temperature and climatic tests, including cold test, dry heat and damp heat conditions, validating performance and durability across extreme temperature and humidity ranges.
- Vibration tests, demonstrating resistance to the mechanical stresses typical of marine applications.
- Thermal runaway non propagation tests, a critical safety requirement.

Thanks to WATTALPS’ immersion cooling technology, thermal runaway is effectively contained, preventing propagation between cells. 

This certification crowns a long and rigorous qualification process and confirms the robustness and reliability of WATTALPS technology for demanding marine environments.

WATTALPS module thermogram

You can see the full article with data tables, illustrations and thermograms with the URL given below.

This TechLetter will focus on WATTALPS battery thermal modeling and the explanation of WATTALPS patented cooling architecture advantage. To illustrate this, we will show simulation results on a sportscar application, for which cell thermal stress can be compared to a battery charge of 80% in less than 20 minutes

Thermal management of batteries is necessary for demanding applications
As explained in our TechLetter on Thermal Management of batteries, lithium-ion battery performance and life are widely influenced by cell temperature. Applications requiring fast charge and/or high power and/or working in extreme temperatures need to be equipped with an efficient battery thermal management system.

Since the performance of the whole battery pack is limited by the least performing cell, the battery thermal management system has to ensure a very homogeneous cell temperature in the whole battery, so as to ensure homogeneous aging and constant performance.

 

Case study
The application selected for this high thermal stress corresponds to a sportscar being driven on a race circuit with an average speed around 140 km/h on a single lap. For the li-ion cells, this is approximately the same thermal stress as charging the battery from 0 to 80% in less than 20 minutes. The vehicle speed and power are shown in the following graphs.

The battery pack used for this simulation is composed of 42 x WATTALPS High Energy modules, a pump and a fluid to air heat exchanger. The battery pack temperature and the ambient temperature are set at 20°C at simulation start. The patented hydraulic architecture of WATTALPS’ batteries enables each modules to be connected in parallel in the hydraulic circuit of the pack. Furthermore, each cell cooling flow is connected in parallel inside each module.

Simulation curves WATTALPS battery module

 

Model definition and parameters
The tools used for the modeling and simulations are:

MAGNA KULI for 1D simulation of full battery system and vehicle.
MAGMASOFT for CFD thermo-fluidics modeling inside 1 battery module
The following steps have been used to progressively refine the model and optimize the system:

Initial System Studies in KULI: simplifications and assumptions to allow comparison of overall design variants and component selection
3D Simulation by MAGMASOFT: enables details on flow distribution and heat transfer coefficients based on 3D design inside one battery module.
Refinement of KULI simulation model with data from MAGMASOFT simulations: to simulate complete operation cycles with a high level of details.
The parameters used in the simulations are derived from characterization tests done by WATTALPS and/or its suppliers.

Simulation results
The step 1 of the simulation process has run with a simplified hydraulic circuit model assuming an ideal flow sharing inside the module. It has led to interesting first results with a battery temperature remaining below 40°C and a maximum temperature difference between cells of 0,4°C in the whole battery. This is very homogeneous and very efficient. Typical cell temperature spread in an equivalent water cooled battery pack is around 8 to 10°C.

Simulation results WATTALPS battery module

From these results, we launch step 2 of the simulation process. WATTALPS’ battery module has been modeled in details with 3D CAD data and the resulting heating power from step 1 has been input in the CFD MAGMASOFT model to check flow sharing, heat exchanges and cell temperature spread inside the battery module. The flow sharing is shown in the following graphs:

Battery module CFD simulation temperature

 

The coolant temperature inside the battery module is illustrated in the following cross section and shows also a very good temperature homogeneity in the module:

Temperature spread inside one battery module CFD simulation

During step 3, these results have been used to refine the MAGNA KULI model and compute more precisely the temperature spread of the cells inside each module and then across the whole battery pack. The results show a very homogeneous temperature with less than 1°C of temperature difference inside the whole battery pack! The cooling power of the air to fluid heat exchanger has been optimized to stabilize the max cell temperature at 40°C, enabling for continuous operation at this highly demanding power profile without overheating cells.

Final simulation result battery module

Conclusion
WATTALPS battery system enables extreme applications to be electrified and keep a long battery life by:

Cooling the cells with an outstanding efficiency
Keeping a very homogeneous temperature in the whole battery, preventing any performance loss due to a badly cooled cell in the pack.
Even with extreme power requirements, the battery pack can be cooled with a simple air to fluid heat exchanger.

 

This TechLetter has been written with the help of MAGMASOFT and MAGNA KULI teams and was presented at ECS conference in May 2023. WATTALPS wants to thank them for their kind contributions.

WATTALPS batteries successfully passed non-propagation of thermal runaway tests

Test Protocol:

A deliberate thermal runaway event was initiated by inducing an internal short circuit in a selected cell—achieved by nailing the cell to trigger uncontrolled self-heating. This method had been checked before to trigger cell thermal runaway in 100% of cases, resulting in cell venting and, in more severe scenarios, in fire or explosion. The goal was to observe the overall battery response to such a critical failure.

Earlier tests were conducted on standalone cells in open air and submerged environments, followed by multiple trials at the module level. For the current qualification test, WATTALPS executed the procedure on a fully charged battery module in the presence of Bureau Veritas. The module was preheated to 37°C, and the test chamber ambient temperature was around 40°C.

 
Key Observations:

> Thermal runaway was successfully triggered in the targeted cell.
> All resulting gases were safely vented through a dedicated safety valve.
> No fire or explosion occurred during or after the event (8 hours monitoring).
> Thermal runaway was contained to the targeted cells and no propagation to other cells of the module, neither to neighboring modules, was observed.
> The temperature of neighboring modules increased by less than 5°C.
> The final battery voltage remained above 90% of its initial value.

These tests were carried out three times on WATTALLPS batteries on three different cells.

WATTALPS Battery system.jpg

WATTALPS Maritime Batteries are based on patented immersion cooling technology which fully immerses the cells, including busbars, in a non-flammable fluid, ensuring unique temperature control and homogeneity across the battery. They deliver:
-High performance (up to 8C power output)
-Certified safety
-Compact size & lower weight (/4) reducing vessel energy consumption
-Fast charging (<15 min) 
-Battery life (4x)
-Modular design making integration into vessels simple and flexible
-Recycling

WATTALPS Maritime Battery Packs

Immersion cooling maritime battery packs certified by Bureau Veritas with Marine Type Approval, for hybrid or full electric vessels.

Advanced batteries - Immersion cooling technology

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