Primary Batteries

Author: E.E. Kimberly

Batteries are of two general types, namely, primary and secondary. When a primary battery such as a "dry" flashlight battery or a "wet" battery of zinc and copper sulfate (obsolete) is constructed, all of the energy which the battery will ever deliver as electrical energy is stored in the constituents as chemical energy. When a circuit is provided between the terminals of such a battery, the current flow is produced by the reaction and decomposition of the chemical reagents. This decomposition and loss of energy is accompanied by an increase in internal resistance.

The open-circuit terminal voltage of a dry battery within the useful life of the battery is practically constant, and hence such voltage cannot be used in determining the physical condition of the constituents. When an attempt is made to draw current from an old used dry battery, the terminal voltage decreases greatly because of internal resistance and the battery is found to be worthless. Recharging is impractical and economically unsound.

When a dry battery produces electric current, the chemical reagent in contact with the electrode surfaces is used up and hydrogen gas collects on the surface of the positive electrode. The collection of hydrogen gas is called "polarization." Because of the slow infiltration of fresh reagent and the slow dispersion of hydrogen, the battery must be allowed to recuperate after a short period of use. For this reason primary batteries of the dry type are fit for only intermittent full duty.