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What Is an Auxiliary Battery Malfunction in a Mercedes? Causes & Fixes

Mercedes Benz

It is no secret that the Mercedes Benz is a marvel of a machine. In fact, it’s one of the handful of modern automobiles with two batteries. The main battery, located under the hood, powers the engine. The auxiliary battery, located in the trunk, powers the Mercedes’ electrical accessories like the radio, navigation system, and lights.

An auxiliary battery malfunction warning means something is wrong with your car’s auxiliary battery. In today’s post, we’ll take a deep dive into what an auxiliary battery malfunction is, what it means for your car, and how you can fix it. But first, what is an auxiliary battery?

car and road divider What Is an Auxiliary Battery?

As mentioned earlier, the Mercedes Benz has two batteries.

The auxiliary battery is a deep-cycle battery designed to provide a steady flow of power over a long period. In other words, the battery keeps your Mercedes’ electrical accessories running even when the engine is turned off.

While the alternator is constantly charging the main battery while you’re driving, the auxiliary battery is only charged when your Mercedes is turned on. That’s why it’s important to ensure that you’re regularly starting your Mercedes, even if you’re not driving it, just to keep the auxiliary battery charged.

What Does an Auxiliary Battery Malfunction Warning Mean?

Generally speaking, an auxiliary battery malfunction warning means that your Mercedes’ auxiliary battery isn’t charging as it should. This can happen for several reasons, but the most common cause is a problem with the car’s alternator.

The alternator is the component that charges both the main battery and the auxiliary battery while you’re driving. If there’s something wrong with the alternator, it can cause the auxiliary battery to become discharged. Discharged batteries are no good because they can’t hold a charge and eventually die.

How Does a Faulty Auxiliary Battery Affect Your Car’s Performance?

Auxiliary batteries are designed to power your Mercedes’ electrical accessories even when the engine is turned off. So, if your auxiliary battery is faulty, it can affect the performance of your Mercedes’ electrical accessories.

For example, if you have a Mercedes with a navigation system, a faulty auxiliary battery can cause the navigation system to malfunction. In some cases, the navigation system may even turn off completely. Other electrical accessories that can be affected by a faulty auxiliary battery include the Mercedes’ radio, Bluetooth system, and lights.

Auxiliary Battery Malfunction: What Should I Do?

If you see an auxiliary battery malfunction warning on your Mercedes Benz dashboard, don’t panic. There are a few things that you can do to fix the problem.

1. Check the Alternator

car alternator
Photo Credit By: Nordroden, Shutterstock

First things first, check to see if your Mercedes’ alternator is working properly. The alternator is located under the hood and looks like a large, black box. If the alternator is faulty, it can cause the auxiliary battery to lose charge and become discharged.

To check if the alternator is working properly, start by turning on your Mercedes. Then, open the hood and look for the alternator. Once you’ve found it, use a multimeter to test the voltage output of the alternator. The voltage output should be between 13.5 and 14.5 volts. If it’s not, then the alternator is likely faulty and needs to be replaced.

2. Replace the Auxiliary Battery

You’ll need to replace the auxiliary battery if the problem is with the auxiliary battery itself. You can usually find replacement auxiliary batteries at your local Mercedes dealership or auto parts store. A replacement auxiliary battery will cost you between $50 and $300, depending on the model of your Mercedes.

When replacing the auxiliary battery, make sure to disconnect the negative terminal of the main battery first. This will prevent any sparks from occurring when you disconnect the battery. Once the new auxiliary battery is in place, reconnect the negative terminal of the main battery, and you should be good to go.

If you’re not comfortable replacing the auxiliary battery yourself, you can always take your Mercedes to a Mercedes dealership or a qualified mechanic and have them do it for you.

3. Perform a Mercedes Benz Auxiliary Battery Reset

In some cases, you may be able to reset the auxiliary battery and get it working again. To do this, you’ll need to disconnect the negative terminal of the main battery for about 30 seconds. This will allow the Mercedes Benz computer to reset and hopefully fix the auxiliary battery issue. Again, you can always take your Mercedes to a Mercedes dealership or a qualified mechanic to have this done for you.

car and road divider Final Thoughts

If your Mercedes Benz is experiencing an auxiliary battery malfunction, don’t panic, there’s always something you can do to get it back in tip-top shape. Remember, most of the time the issue isn’t with the battery itself but with the alternator. A quick look at the alternator with a multimeter should tell you if it’s faulty or not. If it’s, then simply replace it with a new one.

If the problem is with the auxiliary battery, then you’ll need to replace it. You can find replacement batteries at your local Mercedes dealership or auto parts store. Once you’ve replaced the battery, you’ll be good to go.

Featured Image Credit: reverent, Pixabay


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