Climate change represents a significant challenge in the effort to reduce energy consumption. The use of low-temperature residual heat from industrial processes or transport for heating buildings is an interesting solution. For this purpose, efficient heat storage, preferably in portable batteries, is crucial. Phase change materials (PCMs) offer a promising approach because they store heat through phase transitions without significant temperature change. The temperature of the phase change, at which the latent heat is stored in the battery, can be chosen by a suitable choice of active PCM substance, for a specific residual heat temperature. However, PCMs typically exhibit low thermal conductivity, which hinders efficient heat transfer, making battery charging and discharging significantly more difficult. This limitation can be solved by incorporating PCM into properly structured aluminium foam. Heat is thus transferred to and from the active PCM through the cell walls made of highly conductive aluminium, which significantly speeds up charging and discharging. Good heat transfer through the aluminium foam makes it possible to use large volumes of material with a phase change and thereby increase the usable thermal capacity of the battery. The battery of one cubic meter can be charged and discharged with approximately 40 kWh of latent heat keeping the temperature at almost constant level. An innovative patent pending technology addressing challenges such as volume changes during phase transition will be presented.