Water Activated Batteries
These are single use primary cells often called "reserve batteries" with a long shelf life used mainly for emergency applications.
Stored in the dry condition and activated at the time of use by adding or immersing in water or adding an aqueous electrolyte.
Seawater-activated types also available.
Magnesium is generally used as the anode material with various chlorides being used for the cathode cost being traded off for performance, silver chloride having superior energy and current density while while cuprous chloride has lower costs.
Aluminium anodes are also widely used with seawater-activated batteries.
Very high current densities possible.
Light weight without the need to carry the electrolyte.
High power and energy densities
Good response to pulse loading
Long unactivated shelf life
High self discharge rate after activation
Once activated they must be replaced.
Marine use for sonobuoys, life jackets, air sea rescue equipment, emergency lighting, weather balloons.
Forced flow types used for powering torpedoes can deliver over 300kW for 10 minutes
Silver cathode types have high material costs
Non-silver cathode types have low material costs