AGM batteries are better and typically last 6 or more years. The average service life of a wet cell lead-acid car battery is only about four to five years, and can be as little as three years in really hot climates (like Arizona and Florida). #Car battery meter reading how toSee BATTERY REPLACEMENT for details on how to change your car battery. If the battery fails a load test, it needs to be replaced. By comparison, most electronic testers will give reliable test results even if the battery is not fully charged. NOTE: Load testers require the battery to be fully charged for accurate test results. The tester will tell you if the battery is good or bad. This can be done with a hand-held electronic battery tester or a conventional load tester. Charging voltage with engine idling should be 13.5 to 14.5 volts.Īfter the battery has been recharged, the battery should also be tested to see if it is capable of holding a charge. If the current output is not up to specifications, replace the alternator. You should have the alternator tested (or bench tested at an auto parts store). If the charging voltage is less than 13.0 volts, the alternator is not putting out enough voltage and current to keep the battery charged. A charging system that is operating normally should produce about 13.8 to 14.3 or more volts at idle. a fully charged battery will measure about 12.588 volts, and at zero degrees F it will measure about 12.516 volts.)Īfter charging the battery or jump starting the car, connect the voltmeter to the battery the same as before and not the charging voltage. Battery voltage readings willĭrop with temperature roughly 0.01 volts for every 10 degrees F.) (NOTE: these readings are at 80 degrees F. If the battery reads 12.45 volts or less, it is low (less than 75 percent charged) and needs to be recharged. Checking base battery voltage with a voltmeter.Ī fully charged battery should read over 12.6 volts. Select the 12 or 20 volt scale, and connect the volt meter red positive test lead to the battery positive (+) terminal, and the black negative test lead to the battery negative (-) terminal. If the headlights are dim or do not come on at all, you need to check battery voltage and charging output.įor this, you will need a voltmeter. If the headlights come on with normal brightness, the no-crank problem is probably not the battery, but a bad starter relay or solenoid, a poor wiring connection between the relay/solenoid and starter, or a bad starter. One way to do this is to turn on the headlights. The first things you want to check are the battery and the output of the charging system (alternator). The battery needs to be replaced.ĬHECK BATTERY VOLTAGE AND STATE OF CHARGE Your battery is old and will not hold a charge anymore.There is a key off parasitic electrical drain on the battery because a relay is sticking, a module is not shutting down (going into "sleep mode"), or there is a shorted diode in the alternator.The battery is not being recharged while the vehicle is being driven (you have a charging problem).You accidentally left the lights on or some other accessory that pulls power from the battery even when the ignition key is off.What is wrong? WHY A CAR BATTERY RUNS DOWNĪ car battery can run down for any of several reasons: The battery has run down and the engine won't crank. The next morning you go to start your car again, and the same thing happens. Now what? You get somebody to give you a jump start, or you connect the battery to a charger and charge it up until it has enough juice to start your engine. You go to start your car and discover the engine won't crank because the battery is dead. #Car battery meter reading manualsAutomotive Repair Library, Auto Parts, Accessories, Tools & Equipment, Manuals & Books, Car BLOG, Links, Indexĭiagnosing A Car Battery That Runs Down by Larry Carley copyright
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