rting ability and
shall be the capacity in ampere-hours when the battery is discharged
continuously at the 20-minute rate to a final voltage of not less than
1.5 per cell, the temperature of the battery beginning such discharge
being 80 deg.F."

The discharge rate required under the average starting conditions is
higher than that specified above, and would cause the required drop in
voltage in about fifteen minutes. In winter, when an engine is cold
and stiff, the work required from the battery is even more severe, the
discharge rate being equivalent in amperes to probably four or five
times the ampere-rating of the battery. On account of the rapid
recovery of a battery after a discharge at a very high rate, it seems
advisable to allow a battery to discharge to a voltage of 1.0 per cell
when cranking an engine which is extremely cold and stiff.

(f) Temperature. Chemical reactions take place much more readily at
high temperatures than at low. Furthermore, the active materials are
more porous, the electrolyte lighter, and the internal resistance less
at higher temperatures. Opposed to this is the fact that at high
temperatures, the acid attacks the grids and active materials, and
lead sulphate is formed, even though no current is taken from the
battery. Other injurious effects are the destructive actions of hot
acid on the wooden separators used in most starting and lighting
batteries. Greater expansion of active material will also occur, and
this expansion is not, in general, uniform over the surface of the
plates. This results in unequal strains and the plates are bent out of
shape, or "buckled." The expansion of the active material will also
cause much of it to fall from the plates, and we then have "shedding."

[Fig. 25 Graph: Theoretical temperature changes during charge
and discharge]

When sulphuric acid is poured into water, a marked temperature rise
takes place. When a battery is charged, acid is formed, and when this
mixes with the diluted electrolyte, a temperature rise occurs. In
discharging, acid is taken from the electrolyte, and the temperature
has a tendency to drop. On charging, therefore, there is danger of
overheating, while on discharge, excessive temperatures are not
likely. Fig. 25 shows the theoretical temperature changes on charge
and discharge. The decrease in temperature given-in the curve is not
actually obtained in practice, because the tendency of the temperature
to decrease is bala