Calorimeters are used to measure the heat of chemical reaction or physical changes as well as heat capacity. Batteries can be tested in calorimeters to determine the energy density and other characteristics. However, it is difficult to measure these high energy dense systems or to measure the characteristics of complex battery cell configurations such as multiple cells or oddly sized or shaped arrangements. Naval Surface Warfare Center, Crane Division has developed an adaptive heat flow calorimeter that proves flexible and repairable testing capabilities for heat generating or absorbing systems such as energy storage systems. The calorimeter includes a temperature bath adapted to maintain a fluid bath at a predetermined temperature, a containment structure for inserting into the temperature bath, heat sinks, thermal sensor assemblies, an internal containment structure, and thermal barriers between different elements of the invention to isolate different sections from each other. The thermal sensor assemblies and heat sinks are removable so it is possible to measure the heat flow into or out of the containment structure’s different section without being altered by direct thermal contact with other inner sections. Other aspects of this calorimeters design that are an improvement over previous designs include: samples can be rapidly inserted and removed, ability to obtain separate thermal measurements for different section of the sample under test, and capability to insert or substitute components with different sized element to accommodate different types or sizes of samples.