Does your Mercedes-Benz battery slowly drain? Is the battery dead every morning? Does the Mercedes-Benz battery die when you have the car parked overnight or leave it parked for a few days? This step-by-step guide will explain how to troubleshoot this problem, the basics of battery drain problems, why the battery dies overnight, most common trouble spots. You try to start your Mercedes-Benz, and the car is either completely dead, or this happens:
Battery drains happen when electronic equipment (consumer units) constantly draws current from the battery while the car is parked. A straightforward example is when lights are left on overnight. But it’s not always as simple as that. While the electronic equipment in your car should not draw any current when the vehicle is parked, there are exceptions, such as the security system in your car. Even those systems that stay on always draw tiny currents, typically less than 50 milliamperes, and should not drain the battery.
A defective electrical system, Control Unit, or a fault on the CAN Bus (Controller Area Network) also causes that can cause your Mercedes-Battery battery to die.
It would be best to have a multimeter to perform a current reading to troubleshoot the current draw. The multimeter should be able to read at least a 10 amp current. Multimeters are very inexpensive and are purchased for under $20. The Mastech Digital Multimeter is what we use in this guide, it is capable of reading currents, and you can buy it online, click here to check the price on Amazon.
Top 7 Systems that Cause Battery Drain Problems
- Seat Control Module / Power Seat Motor
- Audio System /AGW/amplifier
- Radio/ CD changer/ navigation unit
- Lights, including light in the glove box
- Heated Seat Module
- Proximity Key / Keyless start
- Aftermarket alarm
Before you start troubleshooting battery drain problems
- Make sure you have a fully charged battery.
- Make sure you have the radio code written down. You may be required to enter the radio code after this test.
- You may be required to perform a window and sunroof synchronization.
- If you will keep any of the doors open, manually press the door switch. Find a way to secure the switch pushed in. Use a screwdriver to lock the door latch.
- Manually press the door switch. Find a way to secure the switch pressed. Use a screwdriver to lock the door latch.
- If you have a fuse box in the trunk, open the trunk but place the latch in the locked position.
How to troubleshoot Mercedes-Benz battery drain
Make sure you have a fully charged battery. If your battery is over six years old, you should consider replacing it to avoid further electrical nightmares. You can save on the cost of the battery by purchasing it online. For example, see this list of AGM Group 94 batteries for Mercedes-Benz on Amazon. Turn off the lights. Make sure the dome light is off. Remove any accessories you may have plugged into the auxiliary outlets. Remove the key from the ignition and let the car sit for at least 15 minutes. In some models, you may need to wait up to 30 minutes for all the electronic systems to go “to sleep.” This will allow the car to shut off any electronic consumers that stay on for a brief period after the vehicle is parked.
Locate the battery in the trunk or the engine compartment. Remove the negative battery terminal to connect the multimeter in series, as shown in the next step.
Turn on your ammeter and set it to reader currents on the A setting. Connect one test lead to the battery post and the other to the negative battery cable. You should see a current draw of less than 0.1 Ampere or 100 milliamps. If your read is over this value, we need further troubleshooting. The reading should ideally be under 0.05 ampere.
Locate the fuse box in your car. Disconnect the fuses one at a time. As you remove each fuse, you should check the amperage reading on the multimeter. If the multimeter reading is still high, reinstall the fuse and go to the next fuse. Continue removing and reinstalling all the fuses one at a time until you pull one that makes the multimeter reading drop to below 0.5 A. Once the reading drops below 0.5 amperes, you know that the circuit protected by that fuse is drawing too much current. Then look up the fuse chart to find out which electrical system the fuse protects. For example, it may be the fuse for the seat control module. Next, you must even troubleshoot or replace the seat control module. You may want that fuse removed until you replace the defective parts causing battery drain.
The vehicle must be resynchronized or otherwise normalized after performing this test or anytime you disconnect and reconnect the battery. To synchronize, follow these steps: Open and close the sliding roof and power windows. As the windows and the sunroof reach fully open / fully closed positions, hold the switch down or up for 5 seconds. The steering angle sensor must be reset by turning the steering wheel to full left and full right with the engine running. Clear the BAS/ETS/ESP and other instrument cluster warnings. Follow the direction in the owner’s manual to set the clock and any settings that may have been reset during this test.
If your Mercedes-Benz battery dies, read this article to learn how to jump-start your Mercedes-Benz the right way.
Things to keep in mind
You should eliminate these potential problems before troubleshooting the battery drain problem.
- Make sure no interior or exterior lights are left on during the night. Ensure no lights in the trunk stay on when parking the car.
- Check the battery terminals and ground connections. Clean battery post terminals. Use a battery terminal tool to clean the battery posts and terminals.
- Make sure you don’t have an old battery. Older batteries should be replaced due to age and wear. Perform a battery load test and inspection. AutoZone or Advance Auto Parts will do a battery test for free.
- You should do a visual inspection of the battery. Make sure the battery housing is not distorted. Make sure that all the caps are still on the battery. Check for any leakage if you have an older lead acid battery. Absorbed Glass Mat (AGM) batteries are sealed, and you don’t need to worry about leakage. AGM-type batteries are what newer Mercedes-Benz cars use.
- The voltage Regulator may be defective and needs replacement.
- Test the alternator. Make sure it is generating enough amperage.
- Check that the glove box light does not stay on when the car is parked. The easiest way to check this is to open the glove box after the vehicle is parked for a few hours. Place your hand near the glove box light bulb and feel it if it is warm. Be careful not to burn your hand.
- Aftermarket alarm system. Aftermarket alarm systems are very often the cause of battery drain. They can often discharge a fully charged battery within days, so if you have one of these systems installed, check that first. Maybe disconnect it for a few days and see how it goes. They are often connected to a live battery source with an in-line fuse. Therefore, the test performed in this article may not catch the problem. Locate the alarm fuse, remove the alarm system fuse, and test the current draw for the alarm. It should be less than 0. 1 A.
- The proximity key allows you to walk up to the car and unlock the doors while the key is still in your pocket. A radio receiver in the vehicle continuously listens for a wake-up signal from the key. As the car receives a call in the assigned frequency, it wakes to validate the key. This causes a current draw for several seconds. If the vehicle is left parked in high pedestrian traffic areas, this could be a problem. It may cause the battery to drain within a couple of days in some models. Try to turn off the proximity key function in your car by looking up the instructions in the owner’s manual.
|A Class||W168||1997-2004||A160 CDI||A180 CDI||A200 CDI||A170||A200|
|W169||2004-2013||A160 CDI||A180 CDI||A200 CDI||A170||A200|
|W176||2012-Present||A160 CDI||A180 CDI|
|C-Class||W 202||1993-2000||C 220||C 230||C 240||C 280||C 36 AMG||C 43 AMG|
|W 203||2000-2007||C 230||C 240||C 280||C 320||C 350||C 32 AMG||C 55 AMG|
|W 204||2008-2014||C 250||C 300||C 350||C 63 AMG|
|W 124||1984-1995||200D||230 e ce d te||260||E 280||300 E||300 CE||300 D TE||E 320||400 E||E 420||500 E|
|E Class||W210||1995-2002||E 320||E 420||E 430||E 55 AMG||E 300 Diesel|
|W211||2003-2008||E 200 CDI||E 280 CDI||E 300 E320||E230||E 280||E 320||E 350||E 500||E 550||E 55 AMG||E 63 AMG|
|W212||2009-2016||E 200||E 250||E 300||E350||E 500||E63|
|W213||2017 – Present|
|W 140||1993-1999||500 SEC||600 SEC||S 500||S 600||CL 500||CL 600|
|W 220||2000-2006||S 350||S 430||S 500||S 600||S 55||S 65 AMG|
|W 221||2006-2013||S 550||S 600||S 63 AMG|
|CLS-CLASS||W 219||2005-2011||CLS 500||CLS 550||CLS 55 AMG|
|W 218||2012-Present||CLS 250 CDI||CLS 350 CDI||CLS 300||CLS 350||CLS 550||CLS 63 AMG|
|208||1998-2003||CLK 320||CLK 350||CLK 500||CLK 550||CLK 55 AMG||CLK 63 AMG|
|W 215||2000-2006||CL 500||CL 600||CL 55 AMG||CL 65 AMG|
|W 216||CL 550||CL 600||CL 63 AMG||CL 65 AMG|
|SLK||R 170||1998-2004||SLK 230||SLK 320||SLK 32 AMG|
|R 171||2005-2009||R171||SLK 280||SLK 350||SLK 55 AMG|
|SL||129||1990-2002||300 SL||500 SL||SL 320||SL 500||SL 600||SL 55 AMG||SL 63 AMG||SL 65 AMG||SL 280|
|R 230||2002-2012||SL350||SL500||SL55 AMG||SL600||SL65 AMG||SL550||SL55 AMG|
|R 231||2013-Present||SL350||SL400||SL550||SL63 AMG||SL65 AMG|
|R-CLASS||V 251||2006-2009||R320 CDI||R 320 BLUETEC||R 350||R 500||R 63 AMG||R 300 CDI|
|M-CLASS||W163||1998-2005||ML 320||ML 350||ML 430||ML 500||ML 55 AMG|
|W164||2006-2011||ML 320 CDI||ML 320 BLUETEC||ML 350||ML 500||ML 550||ML 63 AMG|
|W166||2012-Present||ML350||ML400||ML550||ML63 AMG||ML250 Diesel|
|W463||1978-2009||G 290||G 300 D||G 320||G 350||G 500||G 550||G 55 AMG|