EV Battery Heaters

Why heat an EV battery?

Lithium-ion batteries lose half their rated capacity at 0C and won’t take a charge below -7C (19F). That translates to the loss of half the designed range of your EV, or worse. Caliente EV battery heaters are designed to address this challenge. Our product efficiently brings the pack up to -7C while in plug-in mode so it can effectively take a charge. Once charging is initiated, Caliente heater foils complement the heat that is internally generated to bring the pack to optimal temperature more quickly. The Caliente pad heater can also be used as a quick and safe discharge resistor when power needs to be quickly dissipated off the battery for regeneration or in the event of a crash.

What are my EV battery heating options?

  • ModuleDirect Heater Pads - Simply put, they are the most time-, energy- and cost-effective way to heat a battery. Pads are typically 0.011” (0.28mm) thick and can be applied between cells, wrapped around cells or modules, or bonded to the surface of a cold plate directly under a module. The pads ensure quicker time to temp while achieving better uniformity from cell to cell, and function as a dielectric barrier between cells/modules/plates with minimal impact on cooling performance. ModuleDirect heaters are available in self-regulating PTC (50C, 65C, 80C) for built-in safety, or fixed wattage for higher performance.
  • PTC Fluid Heaters – Self-regulating up to 240 degrees C, can be an immersion heater put into fluid reservoir, or self-contained flow through heater.
  • PTC Air Heaters – Self-regulating up to 240 degrees C, primarily used for cabin heating, but can be used for heating battery pack.



How do I specify a ModuleDirect heater pad?

  • Voltage and Wattage – Caliente can design to nearly any input voltage, including 800V. We follow UL standards for isolation to provide a safe design. The wattage depends on the thermal conductivity and mass of what it will be bonded to. The better the conductivity and mass, the higher the watt density (3+ watts per square inch).
  • PTC or Fixed Wattage - Do you want the built-in safety of a self-regulating PTC design, and if so, at which temperature do you want to regulate? Or do you want more performance in time to temperature that a fixed-wattage heater will provide? In the case of fixed wattage, Caliente works with customers to identify optimal sensing and control protocols.
  • Thermal Interface Material (TIM) - One advantage of ModuleDirect heater pads is their thinness/efficiency. At .011”/0.28mm, they have a negligible effect on cooling performance when bonded between a cold plate and a module using a pressure sensitive adhesive. At the same time, it may require a thermal interface material (TIM) to overcome tolerances in the module and/or plate. Caliente can provide heaters with TIM bonded to the heater to lower customer assembly operations and costs.

How does Caliente protect against the potential for air bubbles during application?

The argument against pad heaters has been the labor cost associated with bonding them without capturing air bubbles, which can lead to hot spots and even burnouts. Caliente has developed proprietary materials, designs, processes and tests to ensure they can be applied both cost effectively, and without air bubbles.

Use Case

A recent project saw a 40% energy drop from 4500W to 2700W, and cost from $40 to $25 per pack, while improving time to temp 30% (1 degree C per minute). The heater pads weigh considerably less (flow through heater ~3kg) and occupy significantly less space than a finned air heater, immersion or flow through heater.


  • Energy efficiency (up to 50% less)
  • Better uniformity of heat from cell to cell
  • Faster pack time to temp
  • Lower weight and space
  • Lower cost
  • Also functions as dielectric film


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