Bran new battery died after on 12 hrs overnight.
 

If the compressor is constantly running, sure, of course that can kill a battery. Sounds like maybe the relay is sticking closed, thereby causing the pump to run. Try changing the relay.

Edit: Forgot to add... If the compressor was running, though, I'm surprised you didn't get an overheat message... or the compressor didn't just up and die. Either way, something is not right as it shouldn't be making whatever clicking sound that is that you're talking about. Pull fuses/relays till the sound stops - that will ID the circuit. If you can positively ID where the sound is coming from ahead of time, that will make things easier/faster.

If the problem turns out to be a sticking relay, simply replacing the relay will fix the issue (as long as nothing else is also causing an issue). But again, it's unlikely the actual compressor is running.

First, though, gotta find where that clicking is coming from.

Started it back up pulled the fuse charged it to 95% let it sit overnight dead again in the morning. I'm lost as to what to do? When you say, a sticky relay where would I find the relay? Any clue?

I found this under Mercedes 2011 GL RElay replacement is this what you are talking about? https://www.ebay.com/itm/Mercedes-Be...4383.l4275.c10

charge battery
Install battery
Use amp meter to check what your standby draw is with key far away.

If you find it over 1 amp or so then start pulling fuses until yuo see it drop a bunch.
Make note of how much it drops for each fuse.

The fuse with the most drop has something wrong and that is where you look first.

A relay is different than a fuse. A relay is like a switch. The link that YGMN provided shows a picture. The compressor relay is under the hood, starboard side (along with some other relays). Check your fuse/relay diagram for which one it is (or Google for that).

Last night, was it still making that clicking noise? Did you find where it was coming from? Did you pull fuses/relays till the sound stopped to ID the possible offending circuit? Does the battery weaken even if it's not connected to anything?

Relay
 

Let's eliminate another variable. I know you said it's a new battery, but we want to be SURE it's not faulty. Get it FULLY charged and then take it to a place like Autozone and they can load test it.

If you put that fuse back in, does the sound start up again?
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Short of finding the culrpit via a noise or other obvious way, you can do an amp draw test (mentioned above, or google it) to see how much power is really being pulled once the engine is off and the car "goes to sleep" after X-amount of minutes (maybe 15?). If the DVM is still showing too high of a draw, then start pulling fuses one at a time to locate the problem circuit.

To kill that battery over night (assuming it's healthy and fully charged), you've got a pretty big draw going so the amp draw test will definitely find it.

OK think I'm making progress here. Last night removed the 40 amp circuit breaker for the air compressor and also removed the relay for the airmatic system. Jump started the car ran for one hour turned it off started right back up no issues. This morning it started right up no issues. think I found the problem. Bad relay to the airmatic system. Fix cost so far $20.00 from eEuroparts.com. I will follow up to let everyone know the outcome once the part arrives and is installed.

Battery issue is back after a month of good use.
 

My 2011 450GL has started back doing the same thing it did a month ago. Battery dying overnight. See all the things we troubled shouted before really need some help here to figure this out.

It would seem that you should really test and identify a parasitic draw on the battery. Once you isolate the source, your problem will be much easier to resolve. Here's a video link on how to go about performing the parasitic draw test:

.

And, oh! One last thought: that should be BRAND new battery, not BRAN new. Just sayin'... ..those little details will getcha when your testing for the parasitic draw. :wall:

Found the issue
 

Charged the battery last night. Took the fuse and the relay switch out of the fuse box for the aromatic system. Car started up no issues. It started up all day so I know it’s the aromatic system. What I do t know what’s causing it. Any clues? I replaced the air compressor & block value several months ago, it started a month after they were replaced. I didn’t replace the relay switch which I have ordered. The dealership said they always replace the relay if the replace the air compressor. So I will start there.