BA-2

Dry, 22.5 Volts, 15 cells in cardboard box, Eveready No.763, (NOTE modern battery has screw terminals instead of wire.)

Description

BA–2.—This battery is made up of 15 small cells connected in series and contained in a waterproof cardboard box. The box is sealed on top with a sealing wax or compound, through which the two terminal wires extend, the positive one being red and marked with a plus sign, and the negative one black and marked with a minus sign. Each cell is wrapped in paper and is separated from the other cells by cardboard, thus providing the necessary insulation between the individual cells and also between all the cells and ground. The carbon terminal of each cell is tipped with a brass cap and the cap of each cell is connected by a soldered wire to the top edge of the zinc can of the next cell, thus connecting them all in series. Each cell is about 2-1/8 inches long and 5/8 inch in diameter. The over-all dimensions of the battery are: 2-3/32 by 3-7/16 by 2-19/32 inches high. The weight is about 15 ounces or 0.9 pounds. The battery has an open-circuit voltage of 22 volts; an internal resistance of 6 ohms, increasing to , nearly 10 ohms as the battery approaches exhaustion; a shelf life of 3 months; and a service life of 60 to 100 hours. A single cell has therefore an open-circuit voltage of 1.46 volts, and an internal resistance of between 0.4 and 0.06 ohms. The cells are of such a small size that they would be seriously damaged if the internal resistance and short-circuit current were measured in the usual way by connecting the battery directly to an ammeter. For this reason the internal resistance is measured with an external resistance in circuit (see par. 13 b) and from this data the short-circuit current can be computed to be about 2.7 amperes. The battery was specially designed for use in the plate circuit of vacuum tubes in portable radio sets. Thus the cells are not of a commercial type and the demands for a very small battery made it necessary to sacrifice efficiency and life. The short life of this battery is due to (1) the small amount of chemicals that may be contained in the small size of can; (2) the fact that the process of manufacture can not be as good as in the larger size of cells; and (3) a failure of any one of the 15 cells may cause a failure of the whole battery. In handling this battery care must be taken not to allow the terminal wires to come in contact with each other and thus short-circuit the cells, as this would exhaust them very quickly on account of their small size. When the cells are not in use, the wires should be coiled up on top of the battery where they come out of the wax. The wires should not be cut off, as this may make them too short for connections in some of the sets