Sometimes you get into your car and find that the engine won't start and the headlights won't turn on. After you have started the car with jumper cables, it is wise to determine as soon as possible whether you need a new battery or alternator. Follow these steps to test your car battery.
Steps
Method 1 of 3: Testing your battery with a voltmeter
Step 1. Turn off the ignition
Step 2. Remove the positive battery terminal cover
Visually check and clean the battery terminals.
Step 3. Connect the positive lead of the voltmeter to the positive battery terminal
The positive wire is normally red.
Step 4. Connect the negative lead of the voltmeter to the negative battery terminal
Step 5. Read the voltmeter
If the battery is in good condition, the voltage should be between 12.4 and 12.7 volts. Lower than 12.4 volts means your battery needs to be charged.
- If the meter indicates that the voltage is lower than 12.2 volts, you must charge the battery with a trickle charger, which charges the battery slowly. Check the voltage again after this.
- If the meter reads more than 12.9 volts, the voltage is too high. Then turn on the high beam to get the voltage back to normal. A voltage that is too high can indicate an alternator that is charging the battery for too long.
Method 2 of 3: Checking your battery with a circuit tester
Step 1. Remove the cap from the positive battery terminal
Step 2. Connect the positive lead of the circuit tester to the positive battery terminal
The positive wire is normally red.
Step 3. Connect the negative lead of the voltmeter to the negative battery terminal
Step 4. Connect the very tip of the probe to the positive battery terminal
Read the voltage.
Step 5. Read the measurement
If the battery is in good condition, the voltage should be between 12.4 and 12.7 volts.
Method 3 of 3: Checking your battery by starting the engine
Step 1. Crank the engine by turning the ignition
When the starter motor starts working, keep cranking for two seconds. Ask someone to turn the ignition key while you can read the voltage dip.
Step 2. Read the circuit tester reading while starting
The voltage should not be less than 9.6 volts.
If the voltage read is lower than 9.6 volts, it is a sulphated battery. The load cannot then be held properly
Tips
- Most batteries last 4 to 5 years. In warmer climates, that's only three years. If a charged battery loses voltage without the engine running, it is time to replace the battery.
- After replacing your battery, you must dispose of the old one properly. If unsure, call your municipality. You can usually drop off your old battery at a car supply store.
- You can usually have your battery tested and charged at a car supply store.
- Check your entire system thoroughly before purchasing a new alternator.