TM 116140203141
tery during charge. This ratio is always less than 1;
ple, a 20-ampere-hour battery that is fully discharged
therefore, excess charge must always be returned to
should be recharged at constant current until at least
the battery after discharge to restore rated capacity.
1.25 times 20 ampere-hours are restored, or at least 25
The total charge necessary may be as low as 110 per-
ampere-hours are returned. In general, a 40 percent
cent, or much greater, depending on the temperature
overcharge is recommended, particularly when cell im-
and cell characteristics. It is generally recommended
balance has occurred, charge rates are at the 5-hour
that the nickel-cadmium battery be charged (constant
rate or lower, and the temperature is above 90F.
current) for a time that will give at least 125 percent
210. Gassing
of the previously discharged ampere hours. For exam-
During charge, the tendency of nickel-cadmium cells
to gas increases with temperature rise and the charge
state. Cell gassing characteristics will also vary some-
what among manufacturers, cell types and for various
other reasons. A certain amount of gassing is neces-
sary for a battery to become fully charged. The danger
is in excessive or violent gassing, leading to possible
explosion, loss of electrolyte, or damage to the battery.
Monitor the charging procedure to insure that exces-
sive or violent gassing is controlled by reducing charg-
ing current or charging voltage.
An inherent characteristic of nickel-cadmium battery
cells is that the electrolyte is absorbed within the
plates and separators to a point where it is not visible
from the top of the cells when at a low state of charge
or in a discharged condition. When the battery is re-
charged, the electrolyte level rises and reaches its max-
imum height at full charge. Ideally, the electrolyte
level should be checked on a fully charged battery that
has been at rest for at least 30 minutes and not exceed-
