Merging the expertise in coordination chemistry, thermochemical energy storage materials and microfluidic reactor design yields a novel approach to a modular waste heat and recovery storage device, i.e. a thermochemical heat battery. Based on the synthetic chemical knowledge on transition metal chemistry we investigated salt ammoniates in recent years. To overcome the intrinsic problem of drastic volume work upon ammoniation of anhydrous copper sulphate we miniaturized the system achieving a unique surface-to-volume ratio in µg-scale and embedded and suspended the copper sulphate in a polymer matrix. After proof-of-principle we optimize the microfluidic chip design to develop a modular device, which can be stacked into chip packs thus representing a novel thermochemical energy storage system working as rechargeable heat battery.