CAPACITY OF BATTERIES
reading is lowered. When the electrolyte is cooled, it
contracts and becomes denser, and its specific gravity
The capacity of a battery is measured in
reading is raised. In both cases, the electrolyte maybe
ampere-hours. The ampere-hour capacity is equal to the
from the same fully charged storage cell. As you can
product of the current in amperes and the time in hours,
see, temperature can distort the readings.
during which the battery is supplying this current. The
Most standard storage batteries use 80F as the
ampere-hour capacity varies inversely with the
normal temperature to which specific gravity readings
discharge current. The size of a cell is determined
are corrected. To correct the specific gravity reading of
generally by its ampere-hour capacity. The capacity of
a storage battery, add 1 point to the reading for each 3F
a cell depends upon many factors, the most important of
above 80F and subtract 1 point for each 3F below
these are as follows:
80F.
The area of the plates in contact with the
electrolyte
Adjusting Specific Gravity
The quantity and specific gravity of the
Only authorized personnel should add acid to a
electrolyte
battery. Never add acid with a specific gravity above
The type of separators
1350 to a battery.
The general condition of the battery (degree of
If the specific gravity of a cell is more than it should
sulfating, plates buckled, separators warped,
be, you can reduce it to within limits by removing some
sediment in bottom of cells, etc.)
of the electrolyte and adding distilled water, Charge the
The final limiting voltage
battery for 1 hour to mix the solution. Then take the
hydrometer readings. Continue the adjustment until
you obtain the desired true readings.
STORAGE BATTERY RATING
Storage batteries are rated according to their rate of
Mixing Electrolyte
discharge and ampere-hour capacity. Most batteries
(except aircraft and some used for radio and sound
The electrolyte of a fully charged battery usually
systems) are rated according to a 1 10-hour rate of
contains about 38 percent sulfuric acid by weight or
discharge--that is, if a fully charged battery is
about 27 percent by volume. In preparing the
completely discharged during a 10-hour period, it is
electrolyte, use distilled water and sulfuric acid. New
discharged at the 10-hour rate. For example, if a battery
batteries may be delivered with containers of
can deliver 20 amperes continuous y for 10 hours, the
concentrated sulfuric acid of 1.830 specific gravity or
battery has a rating of 20 x 10, or 200 ampere-hours.
electrolyte of 1.400 specific gravity. You must dilute
Thus the 10-hour rating is equal to the average current
both of these with distilled water to make electrolyte of
that a battery is capable of supplying without
the proper specific gravity. For diluting the acid, you
interruption for an interval of 10 hours. (NOTE:
should use a container made of glass, earthenware,
Aircraft batteries are rated according to a 1-hour rate of
tubber, or lead When mixing electrolyte, ALWAYS
discharge.) Some other ampere-hour ratings used are
POUR ACID INTO WATER-- never pour water into
6-hour and 20-hour ratings.
acid. Pour the acid slowly and cautious] y to prevent
excessive heating and splashing. Stir the solution
All standard batteries deliver 100 percent of their
continuously with a nonmetallic rod to mix the heavier
available capacity if discharged in 10 hours or more, but
acid with the lighter water to keep the acid from sinking
they will deliver less than their available capacity if
to the bottom. When concentrated acid is diluted, the
discharged at a faster rate. The faster they discharge,
solution becomes very hot.
the less ampere-hour capacity they have.
As specified by the manufacturer, the low-voltage
NOTE: Only use and store premixed electrolyte on
limit is the limit beyond which very little useful energy
U.S. Navy ships. The use and storage of acid for the
can be obtained from a battery. For example, at the
purpose of preparing electrolyte or for the adjustment of
conclusion of a lo-hour discharge test on a battery, the
specific gravity are authorized only for shore activities
closed-circuit voltmeter reading is about 1.75 volts per
or for ships designated as intermediate maintenance
cell and the specific gravity of the electrolyte is about
activities (IMAs).
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