Battery Testing
A car battery is a 12-volt lead-acid device that provides the large burst of current (250–1,000 cold-cranking amps, CCA) needed to start the engine and powers electronics when the engine is off. Battery condition degrades through sulfation of the lead plates, water loss, and internal short circuits. A simple voltage test with a digital multimeter tells part of the story: a fully charged 12V battery should read 12.6–12.7V at rest (surface charge). 12.4V indicates approximately 75% charge; 12.0V is 25%; below 11.8V is considered fully discharged. The critical test, however, is the load test — measuring voltage while applying a load equal to half the battery's CCA rating for 15 seconds. A good battery maintains above 9.6V under load; a failing battery drops below 9.6V or shows rapidly declining voltage. Many auto parts stores (AutoZone, O'Reilly, Advance Auto) offer free battery load testing with a dedicated battery tester. Check the battery's age — most lead-acid batteries last 3–5 years in moderate climates, 2–3 years in hot climates (heat accelerates water evaporation and plate corrosion). Inspect the battery case for cracks, swelling (indicates overcharging), and corrosion on the terminals. White or blue-white powdery buildup on terminals is corrosion from hydrogen gas — clean with a terminal brush and a baking soda and water solution.