Lesson 2/Learning Event 2
Remove and inspect the vent plugs to see that the ventholes are open. Use a short length
of stiff wire to run through the ventholes to make sure they are not plugged, but be
careful not to damage the check valves in vent plugs on waterproof batteries.
Inspect the electrolyte level and add water if it is low. Filling instructions are located on
the vent plugs or the cell covers. When correct, the electrolyte level will be at least 3/8
inch above the plates. Distilled water should be used to fill batteries if it is available; if it
is not available, the second choice is rainwater.
Do not store battery water in metal containers. Minerals in water from streams or wells,
or from water stored in metal, can damage and shorten the life of a battery. Water that is
used for drinking can be used, but only when distilled water or rainwater is not available.
A battery will be damaged less by clean water that has some minerals than by letting the
electrolyte level drop below the top of the plates.
Check the specific gravity of each cell with an optical battery/antifreeze tester.
Inspect the battery hold-downs to make sure that the batteries are held properly in their
carriers. If a battery is loose, it may bounce around and damage the container or shake
the plates loose inside the cells. On the other hand, if the hold-downs are drawn too
tight, the container may crack.
OPTICAL BATTERY/ANTIFREEZE TESTER
Since the amount of sulfuric acid in the electrolyte decreases as the battery discharges, the gravity
of the battery also decreases as the battery's state of charge decreases. By using a tester, known as
an optical battery/antifreeze tester, to measure the gravity of the electrolyte, we can tell the battery's
state of charge.
The gravity of the battery is affected by temperature. When heated, the electrolyte expands so it
occupies more space. When the temperature drops, the electrolyte contracts and takes up less
space. Therefore, warm electrolyte weighs less than the same volume of cold electrolyte, so warm
electrolyte has a lower specific gravity than cold electrolyte.