amusa

The Auxiliary battery serves as a backup to the main car battery. Not only it's a backup power supply. It also helps to power some electrical components in the vehicle like Eco start/stop function, emergency parking function, lights, audio system, AC, different driving assist functions, etc. Also maintain the main battery from completely discharge. the purpose of a the Auxiliary battery steps in to fill this role until the main battery are fully charged and back online.

If both battery main and Auxiliary been replace. Then I would start checking for parasitic draw on each fuses to see where it's drawing while the vehicle is off. I would start with the WIFI-Bluetooth area then the alarm system. if it's the alarm system. I would check the alarm siren. These are very known issues on the W209 CLK due to being under the fender liner.

gshockxcc

I just finished watching the video linked in this post, and it's definitely the first thing I'm going to try when I get the car home. I like to solve the problem first and not throw money at it by trial and error.
https://mbworld.org/forums/gle-class...ml#post8309265

Summary: using an Amp Hound or similar amp finder, you can test each of the fuses without pulling them, and determine which one(s) may be causing the drain, if there is one. If not, you can conclusively prove that it's a battery problem and not the drain of an ancillary/auxiliary system.

Incidentally, there is also a class action lawsuit over this same issue, If anyone is interested:
https://www.lieffcabraser.com/defect...battery-drain/

gshockxcc

​​​​​​​Roni,
Thought I would share this directly, since you mentioned that you have had so many problems with the batteries. There's a class action lawsuit against MB over this same issue.

https://www.lieffcabraser.com/defect...battery-drain/

Just thought you might be interested.

juanmor40

Another experience with a W166 platform. Sister's ML350 (W166) had a persistent battery drained a few years ago, circa 2018/2019, and after the main battery was replaced, the issue persisted. We never changed the auxiliary battery (which was changed just last week)

By reading through the forums back then, do not recall if MB World or the "other forum", I came across a thread mentioning the KeylessGo system could drain the battery. The symptom was the battery would drain overnight, or within 48 hours if the car was not completely sleeping. Sister noticed that if she double-clicked the keyfob, and the car went to sleep, the battery would survive overnight and the thread I read was related to that issue.

The advice from the thread was to remove the push-start button to shut down the "looking for a key nearby" feature and use the key instead. I removed the push-start for her and the battery is still the same today. Never drained again, and the push-start button is still in the console compartment. Sister does not want to repair the module or whatever is wrong with it.

Just my 2c.

gshockxcc

Good to know. Thank you. It may just be the case that the Aux battery is bad, and making the Main battery work harder when the engine is off. I didn't replace the Aux battery when I did the main AGM, so I'll do that and see if that resolves the issue. If not, then it's time to start testing the current drain from other systems.

juanmor40

Found the thread, in this forum, and revised my dates (getting old I guess)

https://mbworld.org/forums/m-class-w...ml#post7916378

neilpilot

Today, after parking for 4-5 hours in 100F heat, our 2016 GLC300 4matic wouldn't start. There was a low battery notice and, after the initial failed start, a red warning "Power Steering Malfunction, See Operator's Manual". We called MB road assist, but after waiting for 2 hours the flatbed trailer that came was unable to load our car since it was completely dead (brakes set, no power). Then we jumped it with a power booster, it started right up, and we drove it home.

Post voltage was about 13.5 immediately after restart when we finally got back home. At rest, battery is 12.2v and I plan to check it in about 12 hours to determine if there's excess parasitic discharge.

I installed a new AGM battery in April 2022 (40k miles), and we now have 55k miles. I've seen no low voltage messages in the past 1.5 years (15k miles) until today.

Chamz333

there is also a drain especially if you have a sophisticated alarm system and other electronics in the car

neilpilot

Checked battery terminal voltage over 12 hours, and it remained at 12.1-12.2 volts, so I doubt there's a current drain when parked. Remember my start problem occurred after parking for only 4-5 hours. Removed 16 month old battery and Advanced Auto test indicated battery was OK. So something else caused my problem, but I don't know what.

Edit: Just ran OBD II: Engine - P0562, P2050, P24BE, P0458; EPS - B210A, D & F, U103E

Chamz333

have them erase the codes, most error codes is due to low battery certain components need exactly a certain voltage and when you have a battery problem it will throw off a lot of codes

but make sure your battery is topped off before erasing any codes .. if there is truly a problem codes will come back

this what I have noticed with my 3 Benz’s when battery is low enough and I pull the codes.. so I charge them batteries erase the codes and error codes gone


edit: any alarms, other electronics running.. Myself I have them .. so once a month I just top them off .. not a real biggie.. it is a way for me to check other stuff in the car also like fluids etc..

juanmor40

Drain issue:
=========
It is not that simple to measure battery voltage to determine if there is a drain (it is just a step in the right direction). These vehicles have between 30 and 50 different modules. If there is a defective module, its defect may be triggered by a specific sequence in your habits, sometimes even the order you do things is extremely important.
Step 0: Scan the vehicle for DTC, and if it is not obvious from there, next
Step 1: Identify when the drains happen: day, night, using the AC or not? Is the electric brake engaged or not? Is the telematics talking to the mother ship? etc.
Step 2: Instrument the vehicle to measure the drain when the process identified in (1) is followed
Step 3: Isolate the module that is draining "that much" by guessing, or bisection of removing fuses until the drain goes away.
Step 4: Sometimes it is possible to measure the voltage drop across the leg of a fuse if the car is properly set up. Say, fake the doors are closed but keep them open so you do not wake up the computers. Measure once voltage drops once the car is asleep.

Not trivial, and time-consuming.

OBD codes:
---------------
The P0562, and B210A codes are related to low voltage. The others seems to be related to injector, and EVAP system.

I would delete/clear all the code, and see what comes back. If you can get a MB specific scanner, it would help those here to guide you forward if possible.

gshockxcc

I have a lot of pictures and video to add to this process, but I haven't had a chance to get everything compiled for upload. I wanted to get this update out to people to pay it forward for help that I have received from this forum.

1. Turns out that the starting issue was a loose connection on the negative terminal of the new main battery under the front passenger seat. I thought I tightened it pretty well, but it appears that it loosened up after a couple of weeks. When I went to install the 2nd replacement battery, I found that the nut on the terminal was only finger tight. I tightened it up, any everything came to life. As a suggestion to all, if you're having intermittent issues with the battery, or not starting after replacement, I would recommend checking the terminals to make sure that the road vibrations haven't caused them to loosen. It sounds over simplified, but if I hadn't experienced it myself, I never would have thought that it would be an issue.
2. The AUX battery from Autozone DOES NOT FIT. As Chassis stated, get your parts (at least this one) from the dealer. It's about the same price. The AZ battery is the size of one that would fit in a garden tractor or riding mower. The correct battery is about the size of a 20 pack of gum. Once I figured out the Main battery issue, I went ahead and replaced the AUX battery anyway, just to be safe. This is a time consuming process, but not difficult. On my model, It requires removing the driver's side rear seat back and lifting up the carpet. The battery is small enough that you just need to be able to get your hand in there to remove it from the plastic cradle that it sits in.

gshockxcc

Hello all, as promised, this is a low budget video compilation of the process to get to the Aux battery on the 2018 GLE 350. Depending on your year make, and model, your situation may be different. This is my first MB, so I'm only familiar with this one, so far. A couple of disclaimers:

1. I'm a Mechanical Engineer, but I don't know what I don't know about this car. So there may be easier ways to do things than what I have show here.
2. If you have suggestions to do this better the next time around, feel free to offer.
3. Thanks to everyone on this thread who has commented to far. Every bit of information helps. Some people have defective batteries, and it's a bigger problem. Some are just normal wear and tear. All of the information I have collected, and what I'm providing here is an attempt to help people figure out which is which for their own case.

That said, here's the video:
https://rumble.com/v3gamns-2018-gle-...placement.html

Good luck, and happy MB'ing.

E55 KEV

Thanks. I haven't watched yet but I appreciate all your hard work making the video.