Check a Car Battery
You get into your car and discover that the engine won't start and that the headlights won't turn on. After you jump start the car, you should find out whether or not you need a new battery or alternator. Follow these steps to check a car battery.
Contents
Steps
Check Your Battery with a Voltmeter
- Turn your ignition off.
- Remove the battery's positive terminal cover. Check and clean the battery terminals.
- Connect your voltmeter's positive lead to the positive terminal on your battery. The positive lead on a voltmeter is usually red.
- Attach the negative voltmeter lead to the negative battery terminal.
- Check the voltmeter. If your battery is in good condition, the voltage should be between 12.4 and 12.7 volts. A reading lower than 12.4 volts means that your battery needs to be charged.
- If the reading is lower than 12.2 volts, "trickle charge" the battery, which is a slow charge. And then re-check.
- If the reading is over 12.9 volts, you have excessive voltage. Turn on the high beams to remove excessive voltage surface charge. Over voltage may be an indication the alternator is over charging the battery.
Check Your Battery with a Power Probe
- Remove the battery's positive terminal cover.
- Connect your Power Probe's positive lead to the positive terminal on your battery. The positive lead on a voltmeter is usually red.
- Attach the Power Probe's negative lead to the negative battery terminal.
- Connect the tip of the probe to the positive battery terminal. Check the probe for voltage reading.
- Check the Power Probe reading. If your battery is in good condition, the voltage should be between 12.4 and 12.7 volts.
Check Your Battery by Cranking the Engine
- "Crank" the engine by turning the ignition until the starter engages and hold for 2 seconds Have an assistant crank the engine while you check battery voltage drop.
- At the time of the crank, check the reading of the Power Probe. It should not go below 9.6 volts.
- A battery with a volt reading less than 9.6 volts means the battery is sulfated and not holding/accepting the charge.
Tips
- Most car batteries last between 4 and 5 years. In hot climates, they may only last about 3 years. If you charge your battery and find that it won't hold a charge while your car isn't running, replace the battery.
- If you get a new battery, just be sure to dispose of your old one according to the laws in your state. Usually your auto parts store can take care of battery disposal for you.
- You can test and charge your battery at your local auto parts store.
- Before buying a new alternator, have the system checked more thoroughly.
Warnings
- Never short between battery terminals. Serious burns, damage to the terminals or an explosion from hydrogen gas can occur.
Things You'll Need
- Voltmeter
