Reserve batteries are designed to retain their charge during long storage periods. The electrolyte is kept separate from the rest of battery to avoid self-discharge. This allows the electrolyte to remain inert and makes reserve batteries well-suited for military and aerospace applications. Product specifications for reserve batteries include voltage, capacity in ampere-hours (AH), reserve capacity (RC), energy density, operating temperature, and terminal connections. Choices for terminal connections include button top, screw type, springs, solder, bolt-on, plug-in socket, snap fastener, wire or cable, and other. Width or diameter, depth and height are also important parameters to consider.
Types of Reserve Batteries
There are several basic types of reserve batteries. Magnesium-silver chloride (Mg/AgCl) batteries are seawater-activated primary batteries that offer exceptional reliability and performance. These high-energy batteries can be stored indefinitely, in a wide variety of conditions, with minimal degradation of performance. Because magnesium-silver chloride batteries activate instantly at any temperature and depth, they are often used in sonobuoys, torpedoes, and survival gear. Silver oxide-zinc batteries (Zn/AgO) are also used for military applications. To extend their shelf life, these reserve batteries are manufactured without their electrolyte. Aluminum-silver oxide seawater batteries (Al/AgO) are now under development, and promise power and energy densities of up to 1200 W/kg and 250 Wh/kg.
Reserve batteries include spin-dependent, ammonia, and thermal batteries. With a long shelf life and high performance at low temperatures, spin-dependant reserve batteries are used to power electronic fuses and sensors. Ammonia batteries, as their name suggests, have an ammonia electrolyte. Open-circuit voltages vary from 1.1 to 3.0 V per cell. Thermal batteries are primary reserve batteries that are solid state at normal temperature. For many years, they have been the first choice of power supply for guided missiles and nuclear weapons. Typically, the electrolyte is a mixture of lithium chloride and potassium chloride, which is solid and inert at normal temperatures, but molten at the operating temperature.
Spin-dependent or spin-activated reserve batteries consist of a stack of bipolar electrodes, if high voltage is needed, or a set of alternate anodes and cathodes connected in parallel to give a high current, or a combination of the two. These batteries feature a long shelf life and high performance at low temperatures. Ambient-temperature lithium anode reserve batteries are available in three major types: lithium/vanadium pentoxide, lithium/thionyl chloride, and lithium/sulfur dioxide. Ambient-temperature lithium anode reserve batteries have undiminished power output even after storage periods over fourteen years.