A reserve battery is described that can operate over a wide temperature range, including temperatures as low as −60°C at coulombic efficiencies of 16% or better. The battery is based on the system: lead/fluoroboric acid/lead dioxide and utilizes a bonded lead dioxide cathode. The system is discussed based on data such as: capacities, current‐voltage relationships, and coulombic efficiencies, as a function of temperature; self‐discharge characteristics; specific energy; and cost considerations.