eric roberts

Fix and Find a Car battery Drain

As an apprentice mechanic, I learned a basic routine for diagnosing Car battery Drain complaints from older mechanics. Back then in the late 60,s checking the car’s dome light and courtesy lights inside the glove box, console, trunk, and engine compartment could diagnose 99% of the problems. Obviously, if a bulb was hot after opening the glove box, trunk, etc., then the switch controlling that bulb was stuck closed (shorted).

However, the causes of excessive Car battery Drain have increased over time, and the cost of misdiagnosis can be considerably more than a simple switch replacement. Therefore, it’s essential to take control of the job and maintain control until the vehicle is fixed. This testing requires time and knowledge, and not every motorist is willing to pay for that. Here’s how to diagnose battery drain in your car effectively.

Understanding the Basics of Battery Drain

Before we dive into the testing process, let’s briefly discuss what causes battery drain in a car. In simple terms, anything that draws power from the battery when the engine is off can cause battery drain. Some common culprits include:

Interior lights left on
A faulty alternator
A bad battery cell
A parasitic draw (something drawing power from the battery when the car is off)

Now that we’ve covered the basics let’s move on to the testing process.

Testing the Battery Drain

To test the battery drain, you’ll need a digital multimeter (DMM) or an ammeter, a device that measures the electrical current flowing through a circuit. Here are the steps to follow:

Step 1: Check the Battery Voltage

Before we start testing, we need to make sure the battery is fully charged. To do this, use a voltmeter to check the battery voltage. A fully charged Car battery Drain should read around 12.6 volts. If the voltage is lower, charge the battery before proceeding.

Step 2: Disconnect the Negative Battery Cable

The next step is to disconnect the negative battery cable. This will prevent the alternator from charging the battery and ensure that any current draw is due to a problem in the electrical system.

Step 3: Connect the Ammeter

Connect the ammeter (an instrument used to measure the current in a circuit) between the negative battery terminal and the negative cable that you just removed. This will measure the current draw from the battery.

Step 4: Wait for the Car to Go to Sleep

With the ammeter connected, wait for the car to go to sleep. This means that all electrical systems have shut down, and the car is no longer drawing power from the battery. Depending on the car, this can take anywhere from a few minutes to an hour.

Step 5: Check the Ammeter Reading

Once the car is asleep, check the ammeter reading. A normal current draw is usually less than 50 milliamps (mA). If the reading is higher, there may be a parasitic draw.

Step 6: Locate the Source of the Parasitic Draw

To locate the source of the parasitic draw, you’ll need to start removing fuses one by one while monitoring the ammeter reading. When you remove the fuse that corresponds to the circuit causing the draw, the ammeter reading will drop. This will tell you which circuit is causing the problem.

Finally Conclusion

Diagnosing Car battery Drain in your car is not an easy task, but with the right tools and knowledge, you can do it yourself. However an auto electrician may be required!

The process requires time and patience, but the cost of a misdiagnosis can be much higher than the time and effort you invest in testing. Remember, always take control of the job and maintain control until the vehicle is fixed.

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eric roberts

Managing Director at Pellon Tyre and Auto Centre trading as batteriesontheweb.co.uk

Eric has been the owner of his automotive business for over 40 years now. Running his fast fit and MOT centre in Halifax along with his wife Michelle. Later adding the online battery businesses. Batteriesontheweb,mobilitybatterystore and their Ebay store.

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eric roberts

Fix and Find a Car battery Drain

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