lates and decrease of capacity, and, if the undercharge be great, will
result in a disintegration of the plates. It is, therefore, essential
that the battery be charged regularly and at the rate specified for the
particular battery in question. In order to minimize the chance of
either continuously overcharging or undercharging the battery, the
charges are divided into two classes, namely, regular charges and
overcharges. The regular charges are the periodic charges for the
purpose of restoring the capacity of the battery after discharge. The
overcharges, which should occur once a week or once in every two weeks,
according to the use of the battery, are for the purpose of insuring
that all cells have received their proper charge, for reducing such
sulphating as may have occurred on cells undercharged, and for keeping
the plates, in general, in a healthy condition. The specific gravity of
the electrolyte, the voltage of the battery, and the amount of gasing
observed are all indications of the amount of charge which the battery
has received and should all be considered when practicable. Either the
specific gravity or voltage may be used as the routine method of
determining the proper charge, but, however, if the proper charge is
determined by the voltage readings, this should be frequently checked by
the specific gravity, and _vice versa_.

During the charging and discharging of a battery the level of the
electrolyte in the cells will fall. As the portion of the electrolyte
which is evaporated is mainly water, the electrolyte may be readily
restored to its normal level by adding distilled water or carefully
collected rain water.

_Pilot Cell._ As the specific gravity of all the cells of a battery,
after having once been properly adjusted, will vary the same in all the
cells during use, it has been found satisfactory to use one cell,
commonly termed the pilot cell, for taking the regular specific gravity
readings and only reading the specific gravity of all the cells
occasionally or on the overcharge. This cell must be representative of
all the cells of the battery, and if the battery is so subdivided in use
that several sets of cells are liable to receive different usage, a
pilot cell should be selected for each group.

_Overcharge._ If the battery is charged daily, it should receive an
overcharge once a week, or if charged less frequently, an overcharge
should be given at least once every two weeks. In making an overch