How To Check Your Car Battery (And Alternator)
Updated: Mar 15
Modern car batteries are an amazing piece of technology and from running the radio to starting the motor, it plays a part in many things. So, how can you make sure that a battery is good?
It’s surprisingly simple actually and the 2 methods our mechanics want to tell you about today will help keep your car on the road and make sure the battery and the alternator are healthy.
Firstly, what does a battery and alternator do?
A car battery simply stores electricity to be used by the vehicle when starting the car and when running different systems while the engine is off (such as the radio, lights and windows). The alternator is a little electric generator that refills the battery and provides electricity for the car while the engine is running.
Most modern batteries are 12V (volts) and have cranking capabilities of over 600Amps, an absolutely astonishing amount of power (just like the Rock). On top of this, most modern batteries are also maintenance free, meaning that once they’re in the car, you don’t have to worry about it until you need a new one again.
This leads into the first and easiest test. With the modernisation of batteries (i.e. being made maintenance free), most battery manufacturers have also found a way to create a sight glass in the top which changes colour depending on the health of the battery. Much like a mid-2000’s mood ring, this little sight will show bright green when the battery is ok and bright red when the battery is almost dead.
The best method of test in our minds is actually done using a multimeter which can be picked up from Supercheap for around $30. Set up the meter to read volts DC (very important) and install the red lead on the positive terminal and the black lead on the negative terminal on the battery.
Once you’re set up, you should expect to see around 12V-13.5V with the ignition off. Get a friend to turn on the car and keep an eye on the multimeter. As the vehicle cranks over (just before it’s started), you want to read the multimeter again. For this test you want to see anything over 10V realistically and anything below 10V is a sign of an unhappy battery.
The final test you'll want to carry out is to check the alternator. Really simply, leave the multimeter plugged in the exact same way and read the voltage once more with the engine running. The alternator should charge at around 13.8V-14.5V and a bad alternator can charge far above or below that number.
A bad alternator is by far the worst outcome as, if it fails to charge the battery, the vehicle will only run for as far as the battery can provide electricity. This can cause the car not to start (much like a flat battery or to even stop running, leaving you stranded.
Remember, if you ever have any questions about your car battery, you can always reach out to our Kashy mechanics.