The following rules should be borne in mind by those responsible for the charging of batteries:--

(a) Always charge a storage battery at the lowest rate possible consistent with the time available for charging.

(b) The charging rate can be comparatively high when the battery is in a discharged condition.

(c) The charging rate should be low when the battery is almost fully charged. (Reduce the charging rate when the cells begin to gas freely.)

(d) Never allow storage batteries to get hot (heat is generated in the battery when it is being charged. The nearer the battery is to the fully charged condition, the more heat is generated for a given charging current.)

(C) CARE OF STORAGE BATTERIES USED WITH RCA PHOTOPHONE EQUIPMENT

Two different types of storage batteries are used with Photophone equipment, and the methods of using them are different. Therefore the methods of properly taking care of them differ. The method of caring for these batteries is given separately below.

50. Care of Type MVJ-13 Storage Batteries. -The Type MVJ-13 storage batteries are used on all Photophone equipments where storage atteries are required, with the exception of the PG-1 and PG-2 equipments. The Type MVJ-13 batteries are of the low gravity type and are "manually cycled," i.e., their charging has to be taken care of by the operator.

Keep the outside of the batteries clean and dry.

Keep the separators always covered with electrolyte. Do this regularly by adding only approved water (distilled if necessary). Keep the level of the electrolyte one-quarter of an inch above the top of the plates. Never add acid, or anything else than pure water to the battery.

Use a hydrometer to determine the state of charge of the battery.

The specific gravity of battery electrolyte can be determined by taking the specific gravity reading of one cell, called the "pilot cell." See section 46.

Never discharge an MVJ-13 battery below 1.150 specific gravity, except in an emergency. The specific gravity when fully charged is between 1.200 and 1.220. Do not attempt to bring the hydrometer reading above 1.220 or the battery may be ruined. In some cells the gravity may not go above 1.200. It is commercially impracticable to have the gravity of all cells exactly 1.220 when fully charged, and there is, therefore, a commercial tolerance of 1.200 to 1.220. Determine the "fully charged" specific gravity of the pilot cell by slightly over-charging it (until the specific gravity reading does not change for an hour), and use this figure to determine the state of charge in all future chargings.

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