Book 3 — Testing Dry Cells with Light Bulb

Tests of batteries for telephones, doorbells, and similar appliances, may be made by the use of a lamp from a pocket flash light. Remove the reflector and lamp and connect them with the poles of each cell to be tested, as shown in the sketch. The glow of the lamp is proportional to the amount of life in the cell. Very often but one dead cell will be found to cause trouble. By testing carefully the good cells may be retained and new ones substituted for those worn out.