kle. The active materials themselves are burned and made
practically useless. The hot acid also attacks the grids and the
sponge lead and forms dense layers of sulphate. Such temperatures are
therefore extremely dangerous.

A battery that persistently runs hot, requiring frequent addition of
water, is either receiving too much charging current, or has internal
trouble. The remedy for excessive charge is to decrease the output of
the generator, or to burn the lamps during the day time. Motorists who
make long touring trips in which considerable day driving is done,
with little use of the starter, experience the most trouble from high
temperature. The remedy is either to decrease the charging rate or
burn the lamps, even in the day time.

Internal short-circuits cause excessive temperature rise, both on
charge and discharge. Such short circuits usually result from buckled
plates which break through the separators, or from an excessive amount
of sediment. This sediment consists of active material or lead
sulphate which has dropped from the positive plate and fallen to the
bottom of the battery jar. All battery jars are provided with ridges
which keep the plates raised an inch or more from the bottom of the
jar, and which form pockets into which the materials drop. See Fig.
10. If these pockets become filled, and the sediment reaches the
bottom of the plates, internal short circuits result which cause the
battery to run down and cause excessive temperatures.

If the electrolyte is allowed to fall below the tops of the plates,
the parts of the plates above the acid become dry, and when the
battery is charged grow hot. The parts still covered by the acid also
become hot because all the charging current is carried by these parts,
and the plate surface is less than before. The water will also become
hot and boil away. A battery which is thus "charged while dry"
deteriorates rapidly, its life being very short.

If a battery is placed in a hot place on the car, this heat in
addition to that caused by charging will soften the plates and jars,
and shorten their life considerably.

In the winter, it is especially important not to allow the battery to
become discharged, as there is danger of the electrolyte freezing. A
fully charged battery will not freeze except at an extremely low
temperature. The water expands as it freezes, loosening the active
materials, and cracking the grids. As soon as a charging current thaws
the batte