Flexible Heaters in Battery Thermal Management: Applications and Design Considerations

Introduction

Battery temperature has a direct effect on charging, discharging, power output, and overall system performance.

This becomes especially important in cold environments. When a lithium-ion battery operates at a low temperature, charging capability can be reduced and the battery may require preheating before high-power operation.

This is where flexible heaters become useful.

Unlike rigid heating components, flexible heaters can be designed to match the surface and available installation space of a battery module or enclosure. They can provide controlled heat directly where it is needed without taking up significant space.

For EV batteries and energy storage systems, the heater is not a standalone component. It is normally part of the broader battery thermal management system (BTMS).

Where Are Flexible Heaters Used in Battery Systems?

The location of the heating element depends on the battery structure, thermal path, available space, and required heating rate.

Battery Module Surfaces

For module-level heating, a flexible heater can be attached to the side or bottom of the module.

This approach allows heat to be transferred directly into the battery structure and can be useful when installation space inside the pack is limited.

The design should also consider how heat spreads from the heater to the cells. A heater with high power density does not automatically provide better battery heating if the thermal path is poorly designed.

Battery Pack Enclosures

In some energy storage systems, the heater is installed inside the battery enclosure rather than directly on individual cells or modules.

This approach can help maintain the internal operating temperature of the battery system in cold outdoor environments.

For these applications, environmental resistance becomes particularly important. Moisture, condensation, dust, and temperature cycling all need to be considered when selecting the heater construction.

Areas With Limited Clearance

Battery packs often contain narrow gaps around modules, busbars, cooling structures, and enclosure components.

A conventional rigid heater may not fit these areas.

A flexible heater can be manufactured in a customized shape and thickness, making it easier to use in space-constrained locations.

For extremely limited installation space, polyimide (PI) heaters can be considered because of their thin and flexible construction.

Flexible Heater Selection Depends on the Application

There is no single heater construction that is suitable for every battery system.

The selection normally starts with the installation environment and thermal requirements.

PI Heaters for Thin and Space-Constrained Designs

Polyimide heaters are useful when installation thickness is a major limitation.

Their thin construction allows them to be placed close to the heated surface without significantly changing the mechanical structure of the battery assembly.

This makes PI heaters particularly suitable for compact battery modules and components where available clearance is limited.

For more information, see our guide to PI heaters for EV battery modules.

Silicone Heaters for Harsh Environments

Silicone heaters are often a better fit when the heater needs greater mechanical flexibility and environmental resistance.

They can be manufactured to follow curved or irregular surfaces and are suitable for applications where the heater may be exposed to moisture, temperature cycling, or outdoor conditions.

For battery and energy storage applications, see silicone heaters for EV and battery heating.

Heating Uniformity Matters More Than Maximum Temperature

One common mistake in heater selection is focusing only on the target temperature or heater wattage.

For a battery system, where and how the heat is distributed can be just as important as the total heating power.

If one area of a module becomes significantly hotter than another, the resulting temperature difference can affect battery performance and thermal control.

For this reason, heater layout, contact area, thermal interface materials, insulation, and temperature sensor location should be considered together.

Our article Why Temperature Uniformity Matters More Than Average Battery Temperature discusses this design issue in more detail.

Integrating the Heater With the Battery Thermal Management System

A flexible heater should normally work together with the battery's temperature monitoring and control system.

A typical control strategy may include:

Temperature Sensor → BMS / Thermal Controller → Heater → Battery

When the battery temperature falls below the required range, the control system activates the heater. Once the target condition is reached, heating power can be reduced or switched off.

The heater design therefore needs to consider more than electrical power.

Engineers should also evaluate:

• Operating voltage
• Heater wattage
• Heating area
• Target temperature
• Temperature uniformity
• Installation surface
• Available clearance
• Thermal insulation
• Sensor location
• Environmental conditions
• Electrical insulation requirements

These factors determine whether a heater will work effectively as part of the complete thermal management system.

What Engineers Should Consider Before Choosing a Flexible Heater

For a new battery heating project, it is usually more practical to define the application first and select the heater construction afterward.

The key questions are:

1. Where will the heater be installed?
Cell, module, cooling structure, enclosure, or another component?

2. How much installation space is available?
A thin PI heater may be preferable when clearance is very limited.

3. What is the operating environment?
Outdoor energy storage applications may require a more robust silicone heater construction.

4. How should heat be distributed?
The heater layout should support uniform temperature distribution rather than simply maximizing local heat output.

5. How will temperature be controlled?
The heater should be compatible with the temperature sensors and control strategy used by the battery system.

A good heating solution is therefore not simply the heater with the highest power. It is the heater that fits the mechanical, thermal, and electrical requirements of the battery system.

Flexible Heaters as Part of a Complete Battery Heating Solution

Flexible heaters provide a practical way to add controlled heating to battery systems without introducing large rigid heating components.

Their value comes from the combination of flexibility, customized geometry, thin construction, and controllable heat output.

For EV batteries, energy storage systems, and other battery-powered equipment, the right heater design should be developed together with the mechanical structure and thermal management strategy.

FLD provides customized silicone and polyimide heating solutions for battery and energy storage applications, including heater dimensions, voltage, wattage, resistance, lead configuration, and installation requirements.

Contact FLD for a customized battery heating solution.