What is battery thermal management?

Battery thermal management is the control of a battery pack's temperature so it operates within a defined and consistent range. A battery thermal management system, or BTMS, manages how heat is generated, distributed and removed across the pack, using coolant flow, ambient air and, in many cases, refrigerant-based active cooling.

Why does battery temperature matter?

Battery performance depends heavily on temperature. High temperatures accelerate degradation and reduce efficiency, while low temperatures limit power output and affect charging performance. Temperature differences between cells also lead to uneven ageing across the pack.

How does a battery thermal management system cool a battery?

Most systems use a liquid cooling loop, typically a water-glycol mixture that absorbs heat from the battery cells and carries it away from the pack. When ambient conditions allow, the heat passes to the air through a radiator. As ambient temperatures or thermal loads rise, the system switches to a refrigerant cycle that brings coolant below ambient temperature.

What is the difference between passive and active battery cooling?

Passive cooling rejects heat to ambient air through an air-to-water radiator and avoids the additional power input that active cooling needs. Active cooling uses a refrigerant cycle to bring coolant temperatures below ambient, which keeps the battery under control when ambient temperatures or thermal loads are high.

What is the Grayson Thermal Systems BTMS M1?

The BTMS M1 is a compact, self-contained liquid-cooled battery thermal management unit from Grayson Thermal Systems for battery-electric and fuel-cell-electric vehicles. It houses the water pump, header tank, electric expansion valve, fan, control module and refrigerant circuit in one unit, and it mounts on the roof, chassis or vehicle body.

Which hydrogen bus uses Grayson battery thermal management?

The NesoBus, a hydrogen fuel cell bus built by PAK-PCE, the joint venture between Polsat Plus Group and ZE PAK, now runs in service across Poland. Grayson Thermal Systems supplied a compact, roof-mounted battery thermal management system for the platform. Grayson reports that production has passed 100 NesoBus vehicles, with battery temperatures staying stable across stop-start urban duty cycles and varying climates.

Does rapid charging change how a battery needs to be cooled?

Rapid charging generates higher levels of heat in a short time, which often calls for more aggressive active cooling than standard discharge operation. Grayson also describes a software-defined strategy that brings the battery to a lower pack temperature before a rapid charge begins.

What are the technical specifications of the Grayson BTMS M1?

The BTMS M1 delivers up to 5.8kW of cooling at 40°C ambient with a 25°C coolant outlet temperature and 40 l/min flow, plus 3.6kW of electrical heating as standard. The standard voltage range is 420V to 756V DC, with 900V DC capability available. It uses R134a refrigerant, with R407C optional, measures 750mm x 604mm x 438mm and weighs approximately 55kg excluding coolant.

How does the Grayson BTMS M1 connect to vehicle control systems?

The BTMS M1 uses a CAN J1939 control interface, the SAE International recommended practice for heavy-duty vehicle networks. Grayson configures set-points and CAN addresses at the factory for each customer. Fault codes and status messages broadcast on the network for diagnostics, and a CAN J1939 bootloader allows software updates in the field without disassembly.

What certification and supply details apply to the Grayson BTMS M1?

Grayson lists EMC certification to UN Regulation 10 for the BTMS M1. That regulation sets electromagnetic compatibility requirements for vehicles and their electronic components. Grayson states that it manufactures the unit across four plants worldwide and supports it with a global aftermarket network for parts, technical assistance and service.

Battery Thermal Management Unit by Grayson Thermal Systems

Grayson’s battery thermal management range covers vehicles, rail and stationary storage

(Image courtesy of Grayson Thermal Systems)

Grayson Thermal Systems has published a guide to battery thermal management in its Grayson Thermal Academy series, drawing on its work with PAK-PCE on the NesoBus hydrogen fuel cell bus and its compact BTMS M1 unit. The M1 brings active cooling, passive cooling and electrical heating together in a single self-contained package that connects to the vehicle’s wider electrical architecture over CAN J1939 and supports high-voltage platforms.

How a battery thermal management system controls pack temperature

A battery thermal management system holds a pack within a defined temperature range by moving heat through a liquid loop, typically a water-glycol mixture that carries heat away from the cells. When ambient conditions allow, the system rejects that heat to the air through a radiator, which avoids the extra power draw of active refrigeration. As ambient temperatures or thermal loads rise, it then switches to a refrigerant cycle that brings coolant below ambient temperature.

Rapid charging adds heat over a short period, which can call for more aggressive active cooling or a software-defined strategy that brings the pack down in temperature before a charge begins. For cold conditions, the M1 also delivers 3.6kW of electrical heating as standard to support cold-weather performance.

Battery thermal management on the NesoBus hydrogen bus

PAK-PCE, the joint venture between Polsat Plus Group and ZE PAK, builds the NesoBus, a hydrogen fuel cell bus now running in service across Poland. The compact, roof-mounted system supplied for the platform suits a high-voltage architecture and strict packaging limits, combining active cooling, passive cooling and heating in one unit. Production has passed 100 NesoBus vehicles, Grayson reports, with battery temperatures staying stable across stop-start urban duty cycles and varying climates.

Integration, communication and certification in the BTMS M1

The BTMS M1 houses the water pump, header tank, electric expansion valve, fan, control module and refrigerant circuit in one unit of approximately 55kg excluding coolant, so installers handle fewer separate components, pipes and wires. Cooling capacity reaches 5.8kW at 40°C ambient with a 25°C coolant outlet temperature and 40 l/min flow, while the standard voltage range of 420V to 756V DC comes with 900V DC capability available. The unit mounts on the roof, chassis or vehicle body.

Control runs over CAN J1939, the SAE International recommended practice for heavy-duty vehicle networks, with set-points and CAN addresses configured at the factory for each customer. Fault codes broadcast on the network for diagnostics, and a bootloader allows software updates in the field without disassembly. The unit also carries EMC certification to UN Regulation 10, which sets electromagnetic compatibility requirements for vehicles and their electronic components.

The wider BTMS range adds R-Series units for rail and S-Series units for stationary energy storage. Grayson plans to cover how these systems connect with wider thermal architectures, including refrigerant strategies and system-level integration, in future Grayson Thermal Academy articles.

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Grayson fits battery thermal management into one compact unit

How a battery thermal management system controls pack temperature

Battery thermal management on the NesoBus hydrogen bus

Integration, communication and certification in the BTMS M1