I've had my 2019 G550 for about 40 months now, and have clocked 16K miles. If anything, its starter battery has probably experienced under-utilization rather than misuse and abuse. I permanently disabled the Auto Start/Stop "feature" shortly after taking delivery, so there's no constart charge/discharge under ordinary driving conditions. Recent weather conditions here in Colorado -- temperatures in the 'teens and about 6 feet of snow during January -- resulted in the G remaining parked in my garage (unheated). When I started it about 4 weeks ago, it cranked a bit slow, but fired right up. Last week I put my Noco 10A charger on it preemptively inasmuch as I was planning to drive it the next day.

After connecting the charger, the charge indication was normal, but when I checked on it about an hour later, the over-voltage light was on, indicating that the battery voltage level exceeded the charger's voltage. Assuming that the battery was OK, I disconnected the charger, but when I attempted starting the G the next morning, it would not crank (although the accessory functions and headlights worked). I put the Noco charger on it again, and an hour later the over-voltage light was again lit, but the G still wouldn't crank. I jump started it without any difficulty, and took it for a 15 minute trip down the highway and back. Then I reconnected the Noco charger, and the battery subsequently charged fully (according to the Noco indicator lights), and upon charge completion, the G cranked and started without difficulty.

When I connected my Foxwell battery analyzer to the OE battery, it indicated a CCA level of about 350 (spec is 850), but this could have been a result of the battery's cold temperature. But the analyzer reported 12.6 volts so there was no defective cell or any other apparent abnormality or deficiency reported.

Nevertheless, cold temperatures separate good batteries from bad batteries, and being fundamentally risk averse, I visited Autozone and picked up a Duralast Platinum H8 (900 CCA) replacement. (I replaced my Jeep JK OE battery with a Duralast Platinum about 2 years ago, and have been satisfied with it.) Replacement was easy -- removed the 4 T40 bolts securing the tie-downs and cargo floor board, disconnected the battery terminals, and removed the hold down bracket at the battery's base, and it lifted right out. Installation of the replacement was as easy. Prior to disconnecting the battery, I connected the Noco charger to the engine compartment charge terminals and set the charger to 12V supply to keep all the G's electrical circuits energized so that that nothing needed re-programming afterwards.

The Duralast battery (made in Germany, BTW) cost $240, and change-out time was less than 30 minutes -- an easy enough and economical DIY fix. The G has cranked normally and started right up 3 times in the past couple days under continuing cold temperatures.

However, I'm still baffled by the odd behavior of the Noco charger and/or the G's behavior. Has anyone conclusively determined that there is a auxiliary battery in the 2019+ G Wagen that might intervene in a charging situation such as this?

 

I recently had my 2019 G550 battery replaced under warranty. The Mercedes app showed "partially charged." After the battery replacement, it shows "Charged" and I still drive it in the same manner. The Mercedes tech said it was a faulty battery.

 

My 21 G63 showed a 12V battery alert, blindspot inoperable, distance control please see operator's manual. It disappeared after restarting the car. I told the dealer about it during my annual a few weeks ago and they replaced the auxiliary battery, said it was faulty. The auxiliary battery runs the brain of the gwagen.

 

Use a battery tender. My experience with modern cars and the G wagen in particular is that the always-on electronics drain the battery very quickly. If the battery is not on a tender(charger) my G550 battery falls below 12 volts after just a few days. I leave it on the tender all the time because I have a lot of cars and the G550 doesn't get much use. When any lead acid battery goes below 12 volts for an extended length of time it is suffering some permanent damage. In fact when cars sit on the ship coming over from Germany and in storage at the shipyard and at the dealer they get some battery damage. I've seen dealers have to replace new batteries thinking they're defective when they were just killed by not being charged often enough. I have a Bosch battery in an S class that's still fine after 7 years partly because it's on a charger when not being driven.

 

Makes sense, and likely what happened. I bought mine used.

 

I've been wondering if my '19 G550 has an aux battery. Any idea where it is located?

 

streborx, there is no physical aux battery, i.e., a second battery tmk.

 

I'm confused -- how did the dealer replace Venom-AMG's aux battery if there isn't one?

 

It's not a physical battery but more of a module located somewhere behind the passenger glove box.

 

I think there was a post about this module quite some time ago on the forum. Correct -- it's not a battery, but perhaps some storage capacitor that holds enough juice to keep some essential vehicle services operating in the event of a discharged starter battery. And this module is apparently susceptible to failure. Thanks for the insight.

 

This is what was done

 

Thanks for sharing this. My reading of the repair sheet is that the main starter battery was replaced. Premature failure is unusual, but not unheard of.
Glad to see your front wiring harness recall inspection was OK. Still need to reschedule mine.

 

Before that service I would get fault codes. No blindspot assist, no distance assist,, also the auto stop start didn't stop anymore(good thing). Now the stop/start does it at every light. Haven't seen a code since.

 

There are a handfull of parameters that control the Auto start/stop function, and the starter battery condition is one of them. If the system determines that the starter battery can't handle restarts due to a low charge state, Auto start/stop gets inhibited.