I have a 07 r320 deisel that my father left me. I've replaced the battery because it would not have enough power to start, but it still seems to drain.

My radio can be powered on without even starting the car if I push the button at anytime even without the key in the ignition, I just have to open the door and I can push it on.

I've tried to pull the #25 fuse and have taken off the negative battery terminal to reset this but can still turn the radio on at anytime.

I was wondering if there was a relay or something to stop this, and where it would be located or if anyone knows of any other reasons the battery can drain in this type of vehicle. I would really appreciate it

When you unlock the doors, the vehicle basically powers up. It has a huge amount of electronics that can draw power, the best thing to do is raise the passenger floor up and measure the current draw at the battery and refer to Mercedes dealer for info, I would not be surprised to find it has a draw all the time. How long does the battery stay charged? I find after a few days mine barely starts, it turns over slowly no matter the outside temp, but I am in and out of the car frequently without starting it. It does start, but I hear it turning over slow.
The radio operation is normal, it should turn on without the key.

You will need to find the source of the draw. Put a multimeter in series on the negative side of you battery. Leave it in a place you can see from outside the vehicle. Open the hood. Close all the doors and lock them. Wait about 20 minutes for the car to go into sleep mode. You will see a drop in the amps being drawn. Now read the multimeter. You should see a 30-50 milliamp draw. If it is more than that, go under the hood and pull one fuse at a time and read the draw. Continue until you find the parasitic draw.

If the fuses under the hood are not the culprit, you will need to check the in the car. There should be one fuse panel on the passenger by the door and a second in the back by the spare.

You can use a clamp or something to make the vehicle think all the doors are closed and go into sleep mode. Then start the process all over again.

Once you find the circuit that has the draw, you will need to trace it to find the cause.

Good luck and stay patient.

Thanks a lot Brian I will try that. I went to start it this morning and had no power. I gave it a boost but as soon as I turned the vehicle back off it wouldnt start again and I lost all power. Could this be an alternator problem and not just a power drain? The battery is new and tested. I also noticed that the glow plugs indicator no longer shows in my dash and my rear view camera just shows a blank screen now.

It sounds like a parasitic draw. Something continues to draw power while the car is "off". Since the altenator is not running, the battery ends up going dead.

I cannot stress how important it is to wait for the car to "go to sleep". This will take 20-30 minutes with the doors closed and locked. This will show you the actual draw after the car has entered sleep mode. you should have a low draw, 50 milliamps or less.

Once you find the circuit with the draw, you will need to identify what on that circuit is causing the draw. So you are effectively narrowing down your problem.

Good luck. Electrical issues are time consuming; but, not particularly difficult. You should try to find a wiring diagram for the R320. That will help alot.

Generally, running a vehicle 30 minutes or more will charge the battery sufficiently to restart it.

You said the battery was replaced. Was a MB battery used or aftermarket?

If a MB battery was used it's unlikely to be bad this early, but it is possible. If you used an aftermarket battery, it may or may not be good. These vehicles put a lot or strain on a battery, especially if it's a wet battery - which yo ushould not use btw.

I would go into the engine compartment and measure the battery voltage at the jumper post. See what the voltage is before you start it (make sure everything is turned off, including the lights). Start it (jumper if needed). Measure the voltage again. An alternator should produce between 13 and 15 volts. If you are getting 13-15 volts, run the car a good 30 minutes (Personally, I would take it for a drive so it rev's up a bit). Open the hood and then shut down the car. Use the fob to lock the doors, that will put it to sleep. After the car is asleep (you'll see the interior lights drop out), measure the voltage again. You should have about 12 volts. If you have like 9 or 10 the alternator is not providing sufficient charge.

I'm not sure about a MB but I had a Volvo with a Bosch alternator. I was having intermittent battery issues much like you are experiencing. After a week of messing with it, I took the sertentine belt off, spun the alternator to see if it was a bearing or something, While it was freewheeling, I grabbed the pullen to stoop it. The pully stopped but the armature kept spinning for a few seconds. Seems the Bosch has some kind of clutch in it. I was getting enough power to run the car off the alternator/battery but when the alternator loaded up from normal engine draw, it could not spin the armature adequately. I replaced the alternator with a new one - problem solved.

There are a number of "sam" modules that may go bad and stay on. I also had my battery changed when the car died in the garage. A year later it could not start at the airport... long story short they found a defective rear back up sensor SAM module... Your mileage may vary

And then there is that too

Actually, a fully charged 12-volt battery should measure about 12.6 volts (after being at rest for a while after charging). If it reads 12 volts, that is way too low.

http://www.rvtechlibrary.com/battery/bat_volts.htm

… and then there is the second battery - you should know your R has two of them…one to assist the electric shift under the passenger floorboards.

With the number of battery threads popping up, maybe 7 yrs is about end of life for the battery.