A dead battery is one of the most common problems you may run into with your vehicle, but they can sometimes be difficult to diagnose.The electrical system can't support the increased load of operating other electrical things like your headlights or radio.If you look for signs of electrical issues, you can use a multimeter and increase the engine load to see if there is a problem with the battery.
Step 1: You can find the battery in your vehicle.
You need to locate the battery before you can look for signs of damage.The battery can be found under the hood in most vehicles.Many modern vehicles come with a battery in the trunk.It will look like a black plastic box with 2 terminals.Refer to your owner's manual if you don't know where to look for your battery.The manufacturer's website is a good place to look if you don't have a manual.
Step 2: Look for loose connections.
If you want to test your battery against the load of its starter, you need to make sure it has a strong connection.The cables need to be tightened if they can not move on the terminal.Baking soda can be added to a bowl of warm water if the terminals need to be cleaned.Use the mixture to scrub the terminals and then connect them.Use the right sized wrench to tighten the terminals if they are loose.
Step 3: The key should be turned to the accessories.
The dashboard lights should shine just as bright when you turn the key.The battery is likely dead if the dashboard lights don't come on.The battery won't be able to turn over the engine if the lights are dimmer than normal.You can jump start or charge the battery if the lights don't come on.
Step 4: A friend should stand in front of the car if you turn on the headlights.
The headlights will serve as an indicator as you test the battery against the starter.If you want your friend to observe how you start the car, ask them to stand where they can clearly see the headlights.Before you ask your friend to stand in front of the vehicle, make sure it's in park or neutral and the parking brake is on.
Step 5: Start the car and check the headlights.
As you turn the key to start the car, the headlights will dim slightly as the starter is engaged, however, if they dim significantly or completely go out, it means the battery does not have enough charge.A dead battery is likely to cause a vehicle to fail to start or turn over very slowly.There isn't enough power to engage it as a result of a rapid clicking from the starter.
Step 6: The multimeter should be set to 20 volts.
To get a reading for how much electricity your battery can produce, you need to set it to something over 15 volts.It is the closest option for most multimeters.If you don't have an option on your multimeter, choose the lowest voltage that's above 15 volts.
Step 7: The headlights should be turned on for 2 minutes.
If you want to do away with residual charge in the system, you need to make sure you get an accurate reading of the battery's voltage.Leaving the headlights on will suffice.If the headlights don't work for 2 minutes because the battery is dead, that's a failure of the test.A poorly charged battery will need to be replaced.After 2 minutes, turn off the headlights.
Step 8: The multimeter probes should be connected to the vehicle's battery.
Positive and negative connections will be marked on the probes.The red and black probes should be connected to the positive and negative terminal.Some probes are pieces of metal you touch to the terminal, while others are clips you can attach.The positive terminal on the battery may be red.The negative terminal has a black ground cable that will show the negative symbol.
Step 9: Check the reading on the multimeter.
After running the headlights for 2 minutes, the battery should still read somewhere in the vicinity of 12.6 volts on the multimeter.The battery is insufficiently charged if it reads less than that.A slightly higher reading is normal.It will probably not be enough to start the engine.
Step 10: A friend should start the car.
You can watch your friend start the vehicle if you stay near the engine bay and hold the multimeter.It's important to keep the positive and negative probes connected.Before your friend starts the car, make sure the vehicle is in park or neutral and the parking brake is on.Make sure the wires from the multimeter are out of the way before the engine starts.
Step 11: If the voltage drops below 10, watch.
As the car tries to start, the multimeter's reading will drop, but should not fall below 9.6 or so volts.10 volts is a safe standard to use for an inexpensive multimeter.As the car starts, the battery may need to be replaced.When the car starts, the load from the starter will give way to the alternator, which will charge the battery.
Step 12: The reading should go up if you watch the multimeter for 15 to 20 seconds.
The battery should be charged as the engine starts to run.The reading of the multimeter should be higher when that happens.The alternator is failing to charge the battery.The battery will fail if the alternator is not producing a high enough current.Your vehicle's battery can be ruined by a poorly performing alternator.
Step 13: The multimeter is connected and the car is running.
Turn on the headlights if the multimeter reading was good with the vehicle running.In order to sustain the battery, the voltage reading should be higher than 12.6.If the vehicle can't sustain the increased load of additional things like headlights, the battery will need to be replaced and you should also have the alternator tested.While it is in the engine bay, most auto parts stores can test your alternator.