Question: How can I tell if my battery is good or bad?
Answer: The condition of the cell plates inside the battery
determines whether or not a battery is still serviceable. Current
is produced when sulfuric acid in the battery reacts with lead
in the cell plates. As the battery discharges, sulfate accumulates
on the plates and reduces the battery's ability to make current.
The sulfate is returned to solution when the alternator recharges
the battery by forcing current to flow in the opposite direction.
Over time, some of the sulfate becomes permanently attached
to the plates. The sulfate forms a barrier that diminishes the
battery's ability to produce and store electricity. This process
can be accelerated if the battery is run down frequently or is
allowed to remain in a discharged state for more than a few days.
If the plates have become sulfated, therefore, the battery won't
accept a charge and will have to be replaced.
Average battery life is only about four to five years under the
best of circumstances -- and sometimes as short as two to three years
in extremely hot climates such as Arizona and New Mexico. But
the battery may become "sulfated" prematurely if it
is chronically undercharged (charging problems or frequent short-trip driving),
or if the water level inside the battery drops
below the top of the cell plates as a result of hot weather or
overcharging and allows the cell plates to dry out.
BATTERY TESTING
This is something you can't really do yourself, so you need
to take your vehicle to a service facility that has the proper
test equipment. The battery's condition can be determined one
of two ways: with a carbon pile "load test" (that applies
a calibrated load to the battery) or electronically with a special
tester that measures the battery's internal resistance.
Equipment that uses a carbon pile for load testing requires
the battery to be at least 75% charged. If the battery is less
than 75% charged, a good battery may fail the test. So the state
of charge must be checked first, and the battery recharged if
it is low prior to testing. NOTE: The battery does NOT have to
be fully charged prior to testing if an electronic tester that
measures internal resistance is being used.
If load testing with a carbon pile, apply a load that is equal
to half the battery's cold cranking amps (CCA) rating. A good
battery should be able to supply half its CCA rating for fifteen seconds
without dropping below 9.5 volts.
