How to find the causes of a car battery drain?

Article by Christian A., on August 14, 2018

There is no denying that a battery is important in a car. The battery is needed start the engine and is employed in stabilizing, filtering and providing the power for ignition, lights, electrical components and other accessories that need electricity.

Thus, a battery drain is always the dread of any driver. At worst, you won't be able to start your car. If you’re in a hurry to leave the garage for a trip, a drained battery can be your nightmare. Most of the time, a drained battery is caused – not by a malfunctioning battery or alternator -- by an electrical issue. This issue acts like a parasite that draws electric power from your battery. In this case, you car maybe suffering from an issue called parasitic draw or parasitic drain.

How would you know if the battery drain is caused by a parasitic battery draw? There is way to find out. But first, you need these tools and materials: a digital multimeter with a 20 amp fuse (as set to read 200mA), gloves and eye protection.

First, have the battery charged to its full capacity. Disconnect any electrical components or accessory to the battery. Even your phone charger, dashcam or GPS should be disconnected. A charger still draws current from the car battery even if the phone is not connected. Turn off all the lights and shut all the doors. In addition, remove the main fuses for the amplifiers for speakers and subwoofer. Likewise, remove the key from the ignition switch.

Then, attach the AMP meter to the battery, using the correct series. To do this, you should first disconnect the negative battery terminal from the negative post. Then use the amp meter’s positive and negative probes to complete the circuit between the battery terminal and the battery post.

While the test is doable on either the positive or the negative side, it is much safer to do the process on the ground side. Testing on the ground side would prevent any a short to power, which could create a spark and burn the wires.

Now, it is time to read the amp meter. Select 200 mA in the amp section of the meter to determine whether the battery is suffering from parasitic drain. Depending on the manufacturer as well as the number of computers and features the car has, the normal reading should be between 10 mA to 50 mA. If the values exceed these numbers, there could be a parasitic draw.

There are a number of parts or accessories that can cause the parasitic draw. These include:

1. Lights

Some lighting devices like dimming and timed lights remain awake even after those they were supposedly off. Some these lights include those in the glove box and trunk. Try to peek through a closed glove box or trunk to see if the lights remain awake. You can also quickly touch the bulb and feel if it is warm or hot. If the lights remain awake or if the bulb is warm, then they could be the cause of the drain.

2. Proximity keys

A number of new cars come with proximity keys that emit a certain frequency that is readable within a few meters. When the car computer identifies this frequency, it would wake the car up.

Proximity keys allow drivers to unlock and open the doors of a car without inserting the key. But, even if you have no intention of waking up the car, it would still wake up if you’re near it. Although the car would go back to sleep within a few minutes, the process of waking up drains the battery. Nonetheless, you can turn the proximity sensor off by following the owner’s manual.

3. Other causes

Aside from the lights and proximity keys, there are other things that can drain your battery. These include aftermarket alarms and stereos as well as bad wirings.

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Topics: tips, engine



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