Cold temperatures can change the thermal behavior of lithium-ion batteries significantly.
For EVs operating in cold climates, battery heating may be required before charging or high-power operation. A common approach is to add a flexible heater to the battery module.
But there is an easy mistake to make:
Choosing the heater based only on its wattage.
A 200 W heater does not automatically provide better battery heating than a 150 W heater. The actual result depends on how that heat is distributed and transferred.
1. Heat Distribution Matters
Imagine a battery module heated from underneath.
If most of the heater's power is concentrated in a small area, the surface above the heater can become much warmer than the rest of the module.
The average temperature may look acceptable, while significant temperature differences remain.
For battery heating, engineers should therefore consider:
- Heating area
- Power density
- Heater layout
- Thermal contact
- Insulation
- Sensor position
The goal is not simply to generate more heat. It is to deliver the right amount of heat to the right areas.
2. Thermal Contact Can Change the Result
Heat needs a path from the heating element to the battery.
An air gap or poor mounting interface can increase thermal resistance and slow down heat transfer.
This is one reason flexible silicone heaters can be useful in battery applications. Their construction allows the heater to conform to the target surface and be customized around the available installation area.
But the heater material alone is not enough. The mounting method and thermal interface also need to be considered.
3. Sensor Position Is Part of the Design
A temperature sensor only measures the temperature where it is installed.
If the sensor is too close to the heater, it may detect a local temperature increase while other areas of the battery are still cold.
If it is too far away, the control response may become slower.
This means the heater and temperature sensor should be designed together.
A simple way to view the system is:
Battery → Thermal Interface → Heater → Sensor → Controller/BMS
Changing one part can affect the behavior of the entire system.
4. Flexible Heaters Need to Match the Battery Structure
EV battery modules contain cells, cooling components, busbars, sensors, wiring, and structural parts.
The available space for a heater is therefore often limited.
A customized silicone heater can be designed around requirements such as:
- Length and width
- Heater shape
- Voltage
- Power
- Resistance
- Lead-wire position
- Mounting method
This makes flexible heaters particularly useful when a standard heating pad cannot match the battery geometry.
A Better Starting Point
Instead of asking:
“How many watts should the heater have?”
Start with:
“Where does the battery need heat, how quickly does it need to reach the target temperature, and how evenly should the heat be distributed?”
Once those requirements are clear, heater power, geometry, sensor position, and mounting method can be designed around the actual thermal problem.
For a more detailed discussion of silicone heater design for EV battery applications, see the full engineering article on FLD's website.
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