Testing Procedures -
Safety Precautions
Visual Inspection
1) Inspect battery exterior for damage or cracks.
2) Inspect for loose or broken terminals.
3) Inspect for cause of battery damage.
Important - Replace damaged battery after the cause is determined and eliminated.
Check State of Charge
1) Connect digital voltmeter across battery terminals. Read voltage with no current flowing.
2) If voltage is less than 12.45, charge battery.
3) If voltage is 12.45 or higher, check for possible surface charge. Batteries charged or used in vehicle within last 24 hours must have surface charge removed - Proceed to step 4. Otherwise, proceed to load test.
4) To remove surface charge, connect a carbon pile load tester (such as Sun VAT 40) across the battery terminals and apply a load equal to 1/2 the cold cranking amp (CCA) rating of the battery for 15 seconds.* Read battery terminal voltage again. If still 12.45 volts or above, proceed to load test. If not, charge battery.
Verify that electrolyte is above top of plates in each cell prior to charging or load testing. If electrolyte is below plates, battery may explode if charged or load tested. If electrolyte is low, add distilled water to cell to bring to proper level as indicated on battery case.
The proper test of specific gravity involves checking each of the cells in a battery in comparison to one another. If, after fully charging the battery, one or more cells vary from the remaining cells by 0.050 or more, the battery should be replaced. Be certain that the float in the hydrometer floats freely while taking these readings.
In some instances it may not be advisable or possible to use this method to check state of charge. This would include when the battery is still in the car (risking acid spills), or when the battery has non-removable vent caps such as the Subaru replacement batteries. In these cases, an approximation of specific gravity can be obtained using a digital voltmeter. Connect the voltmeter across the battery terminals. Read this terminal voltage or open circuit voltage (OCV) with no current flowing. The numerical value of this open circuit voltage is 0.84 higher than the numerical value of the specific gravity.
Example: A battery is found to have a 12.66 terminal voltage (OCV). 12.66 divided by 6 cells = 2.11 volts per cell.
2.11 Volts per Cell
- .84 Conversion Factor 1.27 = 1.270 Specific Gravity (Approx.)
This information is useful to determine if the battery is sufficiently charged to load test and, if needed, how long and at what charge rate it should be charged.
NOTE: This OCV method is only an approximation. Actual hydrometer readings should alvays be used when possible. Keep in mind that specific gravity affects the freezing point of the battery. This relationship is as follows:
Specific Gravity Freezing Point
1.280 ----- - 90~F
1.250 ----- -62~F
1.200 ----- -15~F
1.150 ----- +5~F
1.100 ----- +19~F
1.050 ----- +27~F
This is especially important for vehicles stored in cold climates. A battery with a very low charge can freeze at +27~F compared to a 3/4 charged battery at - 62~F.
Load Test Battery
Important - Surface charge must be removed, if necessary, before proceeding with load test. See "State of Charge Check."
1) Attach variable carbon pile load test to battery terminals.
2) Apply load test value of 1/2 of CCA rating. At 15 seconds, read battery terminal voltage. Then turn off load.
*NOTE: The OEM battery model identification number is molded
into its top surface. Refer to the following chart for CCA ratings of batteries used in recent years.
Model Number Cold Cranking Amps.
5OD20R-MF 306 CCA
55D23L-MF 356 CCA
55D23R-MF 356 CCA
65D23L-MF 420 CCA
65D23R-MF 420 CCA
75D23L-MF 356 CCA
75D23R-MF 490 CCA
SOA4071110 (Replacement Battery) 525 CCA
SOA4071120 (Replacement Battery) 490 CCA
If battery being tested is not listed above, consult the specification chart in the Service Manual for model number and CCA rating.
3) Determine battery temperature by touch and compare voltage reading with load test table.
4) If voltage is less than table, replace battery. If equal to or greater, return battery to service.