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Discussion Starter #1 (Edited)
Cheers all,

This morning, my ML's battery was flat. Really flat. Remote didn't do a thing (unlock/lock/liftgate), and I had to open the car with the manual key from inside the fob.
The car's alarm went off when I opened the door, the remote wouldn't silence it, and it did silence once I put the fob in the ignition.
Turning the key did nothing, no relays clicking, nothing (didn't notice if interior lights were on).
I put on a jump charger I keep in the truck (very strong, portable lithium unit - Quebec winters are extremely cold reaching -40 some nights). Truck started fine.

Right after this, I noticed that the fog lights were rapidly flashing. At first, I thought this was a notification that the alarm had been triggered.
I let the truck run for a few minutes then shut it off. I locked/unlocked with the fob a few times to see if this would 'reset' the flashing fog lights. It did not.
I started the truck again and observed that the fog lights continued to flash at the same rapid pace.
I drove the kids to school blinking all the way. They are still flashing as I write this.

With a multimeter, I read 11.80V at the service terminals under the hood. That seems low - this battery is only ~18 months old.
I've put the MB-brand trickle charger on (it's all I have for chargers).
(EDIT: voltage is 13.8V when enging running, I hear the alternator under load).

I've read through our forums and it seems that random flashing lights happen for a variety of reasons, but nothing specific enough to chase down.
The closest situation to mine seems to be this thread: https://www.benzworld.org/threads/fog-lamps-flash-after-locking-car.1988217/
I didn't want to revive an old thread unnecessarily, so I started this one.

In this thread, he ended up replacing the battery and his flashing lights went away.

Recent history of the truck:
Just last week, I installed an Avin Android head unit to replace my COMAND unit. Proceded per AvinUSA's (meager) instructions.
In the following days, I noted that the truck cranked a few more times than normal to get going (this truck otherwise leaps into life every time).
(EDIT: forgot to mention, the Avin unit has a setting that allows for the vehicle's battery voltage to be displayed on the status bar - it was reading ~11.5V engine off, ~13.6 engine running)
Yesterday, the truck failed to crank and I could hear the relays clicking, so the battery wasn't completely flat, unlike this morning.
I suspect that the Avin unit fails to shut down completely, runs, and consumes power and draining the battery.
I read in a post I found elsewhere that the MOST unit (fibre optic to analog converter for the Avin unit) should not have both B+ and ACC connected to the B+ (battery, constant power) from the truck; maybe some parasitic drain there.

Regarding the flashing fog lights - does anyone have any idea what this is a symptom of?

I've attached a link to the video of the flashing fog lights so you can see what I see: 2009 ML320 flashing fog lights
 

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You must charge the battery with a trickle charger with both cables disconnected.

Voltage is supposed to be 12.7v eng. off and 14.2 eng. running.

Now you have to remove or disconnect aftermarket Command. Then after the batt. is properly charged and command removed, see if the Fog lights are still flashing.

In any event, remove the fog lamp bulbs to prevent any further drainage.
 

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Discussion Starter #3
Thanks 43sqd - followed your advice, results below.

I've been charging the battery directly (with ground removed) for the last few hours.

I completely disconnected the Avin unit.

I re-connected the battery once fully charged - the fog lights no are no longer flashing.

I re-connected the original COMAND2.5 system - works perfectly.

I did receive an error on the dash - Auxiliary Battery Failure.

Does the Aux battery need replacing or recharging?
 

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Thanks 43sqd - followed your advice, results below.

I've been charging the battery directly (with ground removed) for the last few hours.

I completely disconnected the Avin unit.

I re-connected the battery once fully charged - the fog lights no are no longer flashing.

I re-connected the original COMAND2.5 system - works perfectly.

I did receive an error on the dash - Auxiliary Battery Failure.

Does the Aux battery need replacing or recharging?
When you disconnected negative cable make sure you didn't knock off negative connection for aux battery.

Main battery is 100 AH it needs to be charged @ 10 A for 10 hours.
 

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Discussion Starter #6
When you disconnected negative cable make sure you didn't knock off negative connection for aux battery.

Main battery is 100 AH it needs to be charged @ 10 A for 10 hours.
I actually did disconnect the (-) for the aux battery.

Now a couple of days later, the warning message is gone and all is back to normal.
I'm keeping an eye on this nonetheless.

Many thanks.
 
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