Modern energy storage devices, such as supercapacitors and batteries, have highly temperature-dependent performance. If a device gets too hot, it become susceptible to "thermal runaway." Thermal runaway—or uncontrolled overheating—can ultimately result in explosions or fires. Adopting a well-informed thermal management strategy is necessary for the stable and safe operation of devices. To do this, it is important to understand how certain thermal properties, like heat capacity (Cp), dynamically change during charging and discharging.