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Battery thermal management is usually associated with cooling. But for lithium-ion batteries operating in cold environments, heating can be just as important.
Low temperature can reduce charging performance, available power, and overall battery efficiency. In some applications, the battery needs to be preheated before charging or high-power operation.
This creates an interesting engineering problem:
How do you add enough heat to a battery system without taking up too much space or creating large temperature differences?
Flexible heaters are one practical answer.
The Heater Is Only One Part of the Thermal System
A flexible heater should not be treated as an isolated component.
A simplified battery heating system looks like:
Temperature Sensor → Controller / BMS → Heater → Battery
The heater generates heat, but the thermal performance depends on how that heat reaches the battery.
For example, a 100 W heater does not necessarily provide better heating than a 60 W heater. If the 100 W heater has poor contact with the battery surface, much of the heat may be lost to the surrounding structure.
This is why heater power, installation location, thermal interface, insulation, and temperature control need to be considered together.
Where Should a Flexible Heater Be Installed?
There is no universal installation position.
The right location depends on the battery architecture and the required thermal path.
1. Side of the battery module
A flexible heater can be attached to the side of a battery module when there is sufficient surface area and a suitable thermal path.
This approach can work well when the module structure allows direct heat transfer from the heater to the cells.
2. Bottom of the module
Bottom heating can provide a relatively large contact area and can be integrated with other layers of the battery structure.
However, engineers need to check the complete thermal path. Adding a heater underneath the module does not automatically guarantee uniform cell temperatures.
3. Battery enclosure
For stationary energy storage systems, the heater may be installed inside the battery enclosure rather than directly on individual modules.
This can be useful when the objective is to maintain the internal battery environment above a minimum temperature.
Outdoor energy storage introduces additional requirements, including humidity, condensation, thermal cycling, and mechanical durability.
Why Flexible Construction Matters
Battery packs are densely packed.
A typical design may include cells, cooling plates, busbars, sensors, structural components, and insulation within a relatively small volume.
A rigid heating element may not fit the available space.
A flexible heater can be manufactured to match the required shape and dimensions.
This is particularly useful when the heater needs to:
- Fit into a narrow clearance
- Follow a curved or irregular surface
- Cover a specific area of a battery module
- Avoid other components
- Maintain a controlled heating pattern
The flexibility is therefore not just a mechanical feature. It can directly affect how the thermal system is packaged.
PI or Silicone?
Two common flexible heater constructions for battery-related applications are polyimide and silicone.
Polyimide heaters
PI heaters are useful when thickness and available space are major constraints.
A thin heater can be installed close to the target surface while adding very little thickness to the assembly.
This makes PI heaters interesting for compact battery modules and other applications with limited clearance.
Silicone heaters
Silicone heaters are useful when flexibility, surface conformity, and environmental durability are important.
They can be manufactured in different shapes and can follow curved surfaces more easily than many rigid heating solutions.
For outdoor energy storage applications, the overall heater construction also needs to be evaluated against moisture, temperature cycling, and the expected operating environment.
So the question is not simply:
“Which material is better?”
A better question is:
“Which heater construction fits the mechanical and thermal requirements of this battery system?”
Don't Design Around Wattage Alone
One of the easiest mistakes in battery heating design is selecting a heater based mainly on its wattage.
Consider two heaters:
- Heater A: 60 W
- Heater B: 100 W
It is tempting to assume that Heater B will heat the battery faster.
But the actual result depends on:
- Heating area
- Contact area
- Heater position
- Thermal conductivity of surrounding materials
- Insulation
- Ambient temperature
- Battery mass
- Heating time
- Temperature control
A high-power heater concentrated in a small area may create local hot spots, while a lower-power heater distributed across a larger area may provide more uniform heating.
For battery systems, temperature distribution can be more important than maximum local temperature.
Temperature Uniformity Is a System-Level Problem
Suppose the heater is attached to the bottom of a battery module.
The cells closest to the heater may heat faster than cells farther away.
That means the battery may have an acceptable average temperature while still having a significant temperature difference between individual cells.
The solution may involve changing:
- Heater geometry
- Heating area
- Heater position
- Thermal interface material
- Insulation
- Heating power
- Control strategy
This is why thermal simulation and prototype testing can be useful before finalizing the heater design.
How Temperature Control Fits In
A heater should normally be controlled according to the battery's actual temperature rather than simply running continuously.
A basic control strategy might be:
- Measure battery temperature.
- Compare it with the required operating range.
- Activate the heater when temperature is too low.
- Reduce or stop heating when the target temperature is reached.
- Continue monitoring during charging and operation.
The actual control algorithm can be more complicated when the heater needs to work with the BMS, charging system, and cooling system.
The important point is that heater selection and control strategy should be considered together.
A Practical Engineering Checklist
Before specifying a flexible heater for a battery application, I would define these parameters first:
Mechanical
- Available installation space
- Heater dimensions
- Surface shape
- Mounting method
- Clearance from other components
Electrical
- Operating voltage
- Required power
- Resistance
- Lead configuration
- Electrical insulation requirements
Thermal
- Starting temperature
- Target temperature
- Heating time
- Heating area
- Temperature uniformity
- Thermal interface
Environmental
- Ambient temperature
- Humidity
- Condensation
- Vibration
- Thermal cycling
This information gives the heater manufacturer a much better starting point than simply specifying “I need a battery heater.”
Final Thoughts
Flexible heaters are useful in battery thermal management because they allow the heating element to be designed around the battery rather than forcing the battery structure to accommodate a rigid heater.
But flexibility alone does not solve the thermal problem.
The important engineering questions are:
Where should the heat be introduced?
How will the heat reach the cells?
How uniform does the temperature need to be?
How will the heater be controlled?
Answering these questions first usually leads to a better heater design than starting with wattage or heater material alone.
For engineers working on EV batteries or energy storage systems, FLD develops customized silicone and polyimide heaters based on application-specific dimensions, voltage, power, resistance, and installation requirements.
You can find more information about its battery heating solutions here:
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