(c) Condition of plates. The same troubles should be looked for as in automobile batteries. See pages 339 to 346. An examination of the outside negatives is usually sufficient. The condition of the positives may also be determined if a flash light or other strong light is directed on the edges of the plates. Look for growths or "treeing" between plates.
(d) Condition of separators. See page 346.
If cells have sealed rubber jars, proceed as follows:
(a) Measure height of electrolyte above plates with glass tube, as in Fig. 30. If in any cell electrolyte is below tops of plates that cell is very likely the defective one, and should be filled with distilled water. If a considerable amount of water is required to fill the jar it is best to open the cell, as the plates have probably become damaged. If the jar is wet or the rack is acid eaten under the jar, the jar is cracked and must be replaced.
If you have not found the trouble, make the following tests, no matter whether glass or rubber jars are used:
(a) Measure specific gravity of each cell. If any cell is badly discharged it is probably short-circuited, or contains impurities and had better be opened for inspection.
(b) Turn on all the lamps and measure the voltage of each cell. If any cell shows a voltage much less than 1.8 it is short-circuited or contains impurities, and should be opened for inspection.
(c) Examine the connections between cells for looseness or corrosion; and examine the connections between the battery and the generator, going over cables, switches, rheostats, etc. Make sure that you have a complete and closed charging circuit between the generator and the battery.
(d) If cutout is used on the switchboard, see that its contact points are smooth and clean, and that they work freely.
(e) Run the generator to see if it builds up a voltage which is sufficient to charge the battery, about 42 volts for a 16 cell battery. If the generator is not working properly, examine it according to directions on page 451. Check up the field circuit of the generator to be sure that it is closed. A circuit-tester made of a buzzer and several dry cells, or a low voltage lamp and dry cells, or a hand magneto is convenient for use in testing circuits. Test armature windings and field coils for grounds.