To harvest and reuse low-temperature waste heat, we propose and realize an emergent concept—barocaloric thermal batteries based on the large inverse barocaloric effect of ammonium thiocyanate (NH ₄ SCN). Thermal charging is initialized upon pressurization through an order-to-disorder phase transition, and the discharging of 43 J g ⁻¹ takes place at depressurization, which is 11 times more than the input mechanical energy. The thermodynamic equilibrium nature of the pressure-restrained heat-carrying phase guarantees stable long-duration storage. The barocaloric thermal batteries reinforced by their solid microscopic mechanism are expected to substantially advance the ability to take advantage of waste heat.