Loss of Active Material

The result of shedding, provided no other troubles occur, is simply to
reduce the capacity of the plates. The positives, of course, suffer
more from shedding than the negatives do, shedding being one of the
chief weaknesses of the positives. There is no remedy for this
condition. When the shedding has taken place to such an extent that
the capacity of the battery has fallen very low, new plates should be
installed. After a time, the sediment space in the bottom of the jar
becomes filled with sediment, which touches the plates. This
short-circuits the cell, of course, and new plates must be installed,
and the jars washed out thoroughly.

1. Normal Shedding. It is natural and unavoidable for the positives to
shed. Lead Peroxide is a powder-like substance, the particles of which
do not hold together. A small amount of sulphate will cement the
particles together to a considerable extent. At the surface of the
plate, however, this sulphate is soon changed to active material, and
the peroxide loses its coherence. Particles of peroxide drop from the
plates and fall, into the space in the bottom of the jar provided for
this purpose.

Bubbles of gas which occur at the end of a charge blow some of the
peroxide particles from the plate. The electrolyte moving about as the
battery is jolted by the motion of the car washes particles of
peroxide from the positive plates. Any slight motion between positive
plates and separators rubs some peroxide from the plates. It is
therefore entirely natural for shedding to occur, especially at the
positives. The spongy lead of the negatives is much more elastic than
the peroxide, and hence very little shedding occurs at the negative
plates. The shedding at the positives explains why the grooved side of
the separator is always placed against the positive plate. The
grooves, being vertical, allow the peroxide to fall to the bottom of
the jar, where it accumulates as sediment, or "mud."

2. Excessive Charging Rate, or Overcharging. If a battery is charged
at too high a rate, only part of the current is used to produce the
chemical actions by which the battery is charged. The balance of the
current decomposes the water of the electrolyte into hydrogen and
oxygen, causing gassing. As the bubbles of gas force their way out of
the plates, they blow off particles of the active material.

When a battery is overcharged, the long continued gassing has the same
effect as desc