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AS you stated it is 12 years old. Anything made by man won't last forever. How do you know that the battery is good? Inspect The Battery. Look for obvious problems such as a loose or broken alternator belt, low electrolyte levels, a dirty or wet battery top, corroded or swollen cables, corroded terminal mating surfaces or battery posts, loose hold-down clamps, loose cable terminals, or a leaking or damaged battery case. Repair or replace such items as required. Distilled water should be used to top off the battery fluid level. Measure The State-Of-Charge. To determine the battery's State-of-Charge with the battery's electrolyte temperature at 80° F. The Specific Gravity or Open Circuit Voltage readings for a battery at 100% State-of-Charge will vary by plate chemistry, so check the manufacturer's specifications for a fully charged battery. If there is a .050 (sometimes expressed as 50 "points") or more difference in the specific gravity reading between the highest and lowest cell, you have a weak or dead cell(s). Using the battery manufacturer's recommended procedure, applying an Equalizing charge may correct this condition. If the battery will not recharge to a 75% or more State-of-Charge level or if the built-in hydrometer still does not indicate "good" (usually green or blue, which indicates a 65% State-of-Charge or better). If a digital voltmeter indicates 0 volts, there is an open cell. If the digital voltmeter indicates 10.45 to 10.65 volts, there probably is a shorted cell. A shorted cell is caused by plates touching, sediment ("mud") build-up or "treeing" between the plates. Load Test The Battery. If the battery's State-of-Charge is at 75% or higher or has a "good" built-in hydrometer indication, then you can load test a car battery by applying a load equal to one half of the CCA rating of the battery for 15 seconds. The minimum voltage under load should not be less than 9.7 volts at 80ºF. Bounce Back Test The Battery. If the battery has passed the load test then it should be OK. If not, remove the load, wait ten minutes, and measure the State-of-Charge. If the battery bounces back to less than 75% State-of-Charge (1.225 specific gravity or 12.45 VDC), then recharge the battery and load test again. If the battery fails the load test a second time or bounces back to less than 75% State-of-Charge, then replace the battery because it lacks the necessary CCA capacity.
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