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File description: Car Batteries Your name: (optional) Todd
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Got this info from FAQ on batteries:
The are four simple steps to test a car battery: inspection, remove
surface charge, state of charge test and load test. To test a battery
(or to troubleshoot charging or electrical systems), you will need a
digital voltmeter with .5% or better accuracy. A digital voltmeter can be
purchased at an electronics store and will cost between $20 and $200 U.S.
If you have a nonsealed battery, you will need a temperature compensating
hydrometer which can be purchased at an auto parts store for approximately
$5 U.S.
A. INSPECTION
Visually inspect for obvious problems, e.g., loose alternator belt, low
electrolyte, corroded cable or terminal clamps, loose holddown clamps or
cable terminals, or a damaged case.
B. REMOVE SURFACE CHARGE
If you have just recharged your battery or driven your car, eliminate any
surface charge by one of the following methods; otherwise, go to the next
step:
1. Allow the battery to sit for two to three hours,
2. Turn the headlights on high beam for five minutes and
wait five minutes, or
3. With a battery load tester, apply a load at one half the
battery's CCA rating for 15 seconds and wait five minutes.
C. STATE OF CHARGE TEST
Using the following table, determine the battery's state of charge:
Open Circuit Approximate Average Cell
Battery Voltage State of charge Specific Gravity
12.65 100% 1.265
12.45 75% 1.225
12.24 50% 1.190
12.06 25% 1.155
11.89 0% 1.120
[If the temperature of the electrolyte is below 70 degrees F (21.1 degrees
C), then add .012 volts (12 millivolts) per degree below 70 degrees F to
the reading.]
For nonsealed batteries, check both the specific gravity in each cell
with a external hydrometer AND the battery terminal voltage with a digital
voltmeter without the engine running. For sealed batteries, measuring the
battery's voltage without the engine running with an accurate digital
voltmeter is the only way you can determine the state of charge. Some
batteries have a built-in hydrometer which only measures the
state of charge in ONE of it's six cells. If the indicator is clear or
light yellow, then the battery has a low electrolyte level and should be
refilled before proceeding, or if sealed, the battery should be replaced.
If the state of charge is BELOW 75% using either the specific gravity or
voltage test or the built-in hydrometer indicates "bad" (usually dark),
then the battery needs to be recharged BEFORE proceeding. Replace the
battery, if one or more of the following conditions occur:
1. If there is a .050 or more difference in the specific
gravity reading between the highest and lowest cell, you
have a weak or dead cell(s),
2. If the battery will not recharge to a 75% or more
state of charge level or if the builtin hydrometer still
does not indicate "good" (usually green, which is 65%
stateofcharge or better),
3. If digital voltmeter indicates 0 volts, you have an open
cell, or
4. If the digital voltmeter indicates 10.45 to 10.65 volts,
you have a shorted cell. [A shorted cell is caused by
plates touching, sediment buildup or "treeing" between
plates.
D. LOAD TEST
If the battery's stateofcharge is at 75% or higher or has a "good"
built-in hydrometer indication, then load test the battery by one of the
following methods:
1. Turn the headlights on high beam for five minutes,
2. Disable the ignition and turn the engine over for 15
seconds with the starter motor,
3. With a battery load tester, apply a load equal to one half
of the CCA rating of the battery for 15 seconds, or
4. With a battery load tester, apply a load equal to one half
the OEM cranking amp specification for 15 seconds.
DURING the load test, the voltage on a good battery will NOT drop below
9.7 volts with the electrolyte at 80 degrees F (26.7 degrees C). [If the
electrolyte is above 80 degrees F, add .1 volt for every 10 degrees above
80 until you reach 100 degrees. If below 80 degrees F, subtract .1 volt
for every 10 degrees until 40 degrees.] After the load is removed, wait
five minutes and the battery should "bounce back" to the 50%
state of charge level or above. If the battery drops below minimum test
voltage, does not bounce back, or will not start the engine, then you
should replace it. If the battery passes this test, you should recharge
it to restore it to peak performance.