I just purchased a 2009 SL550 yesterday. Car has 100k miles but has been meticulously serviced and cared for. Around 4 hours after picking the car up yesterday I was unable put the top down and got a notification referring me to the manual. Within another 5 minutes I had a battery/alternator warning show up in the cluster. I drove home and after stopping the car was unable to restart. I charged both the front and rear batteries overnight and now all works as it should. I drove the car for ~40 minutes this morning without any issues.

Would draining the rear battery through excessive electronics/convertible top usage also subsequently drain the front battery? This was my initial question as both batteries were replaced within the past 5 months. This car had been largely unused since last fall. In addition to being at the detailing shop for 2 days prior (where I'm sure the radio was going and doors open), I had opened/closed the convertible top probably 5-6 times yesterday after picking up the car and turned the car on/off probably 4 times.

Would it make sense that my battery issue yesterday was a result of excessive battery usage? Or should I be more immediately concerned about the alternator or other parts of the battery system e.g. voltage regulator? I'm trying to figure out how to go about this as I obviously bought the car as-is, but would escalate things if the dealer knew about a faulty alternator and simply charged up the batteries to get me off the lot.

Addendum: I checked my battery voltage using the secret/engineering menu. Battery voltage was 12v at rest and appropriately rose and stabilized at ~14.2v after starting the car. Drove around for another 30 minutes to ensure stability. I'm assuming this means the alternator is functioning appropriately and I simply overused the battery yesterday? That said, I'm still having an issue with the fact that the convertible top failed yesterday prior to the battery message and whether or not the two batteries are indeed connected...?

 

Welcome to the forum! Nice choice of car.

The voltages sound good for a properly operating charging system.
Why the front battery was dead is a mystery, and could be a number of things like bad battery, battery control module, mega fuses to front battery, or just bad connections. It is only used to start the car.
The roof can fail to operate if the hydraulic pump stops working, or there is not enough voltage, or a number of micro-switches for the top are not contacting. Too much to cover here.

I would continue to drive the car and monitor both battery voltages every day to see how it goes. Sometimes random faults happen, then go away.
If voltages drop, there is an issue somewhere.
FYI - it is NORMAL to lose battery voltage from the rear battery, and I recommend a battery tender for it if sitting more than 3 days.

Keep us posted on the outcome.

 

The SL's ear batteries. I kept on a tender every night.

 

​​ Thanks for the thoughtful response.

As it turns out I had a recurrent battery warning today while driving. I checked the engineering menu on my way home and was able to see that the charging system was not working - voltage was only around 11 and unchanged with stopping and restarting the engine. I called the dealership immediately and spoke with the owner. He told me that the alternator and both batteries had been replaced in the past few months and were under warranty still. He graciously offered for me to bring the car back so it could be inspected and dealt with accordingly. Curious what this intermittent issue is... we'll see.

Thank you, I did order one of these yesterday

 

the sun visor make-up light was on for 2 days. the plastic lid was broken leaving the light on

 

ok, so if both batteries don’t work in tandem—Is it possible to safely jump start an R230 by connecting cables from the house battery to the starter battery.😬

 

If I am corrdect, the SL WILL start off both batteries, if one is low on voltage. But there is some smart managment involved. If all is charged and normal, it will start the motor with the front battery. If the rear battery is low (or empty) and the front is fine, it will start, using the front battery. You will get a message that your comfort electronics are disabled until the rear battery is charged sufficiently. Comfort electronics include the roof, the heated seating etc. If the front battery is low, you will get a red battery warning in the dash. The car will start by using the rear battery.
Then there is the charging. The alternator charges the rear battery only. The front battery is charged by a voltage regulator powered by the rear battery. If your alternator is not working but the rear battery is fully charged, your front battery would still show over 14V beeing charged (while driving) until the rear battery runs low.

 

That shouldn't be on for two days, I have wired my dash cam to the vanity light and I know that the led on the cam stays on for about 5 mins after I lock the car then goes off, telling me the power has switched off too.

 

Do not jump start the battery to the rear, it will damage it, this is what happened to mine as it buckeld a plate and caused it to overheat. It actually states in the manual to only use the front battery, this is the starter battery for the engine.

 

All

I agree the SL's are power hungry but dont think you should need to plug in any battery tenders if your batteries are healthy. It definitely depends on your battery choice, I had bought a brand new OEM battery and it lasted okay for about 4 months, then I started to get the 'Convenience error' message on dash stating that the battery was low, after driving for 10mins all would work once more. However I returned the battery and bought the proper one from Mercedes and never had an issue in 6 months ! During the COVID I have not used my car for 5 weeks, it has sat on the road and started with no issues, I have wired in a digital volt meter and get 12.2VDC at rest and 14.1 when driving so know that the voltage regulator is working correctly. I would suggest getting a proper battery from Mercedes if your charging system is good at 14.2VDC

 

The front battery will start the car even after sitting for many months. The problem is the accessory battery in the trunk will go dead in a few weeks if you don't drive the car and that leads to frequent battery changes. Mine was an OE MB battery. Made no difference.

 

Did the battery have Mercedes Benz labelling etc? strange if that is the case, how long does it take for the 'convenience error' to go from the dash?

 

Uh, yeah, that would be the definition of an MB battery. It would typically take 5 to 7 days for it to give the error and would go away after driven for 3 to 10 miles. After a few weeks, it would almost be completely dead and take much longer for it to charge. It eventually failed completely and was replaced with a non MB battery as was the front. Was a pain to deal with since I liked driving with the top down. Trickle charger solved everything. No more issues after that.

 

If its a proper Mercedes battery you have, then I can't think its battery related and your car must have a fault or power drain from somewhere, there must be a reason why. When you turn your car on, how long does the pump run in the front and likewise for the rear PSE when you open the door or trunk?

Simply connect a multi-meter to your rear battery and run the wires outside the car to monitor the volts or current draw. The battery should sit around 12.4V if its less than this its only at about 3/4 charge, however at 12.6V it will be fully charge, anything less than 12.2V is deemed as dead. Check the voltage after a couple of hours or overnight and see if its dropped any.

Attached are a couple of photos of my old battery, new one cast me £180 but this was with discount as actually was £220 ($278) it should have a hologram etc

 

My battery is at 11.6v with engine off and climbs to 14v within 20 seconds with engine on. Does this mean that my battery is bad and should be replaced soon? The battery was replaced 10 months ago, I bought it a couple months ago, I have a 2009 SL550.

 

One criteria would be how long the battery takes to fall to 11.6 volts and whether or not there is a drain on the battery from an errant component. More important is how the battery performs: "If it ain't broken, don't fix it."

 

"If it ain't broken, don't fix it." is a golden rule! I wouldn't have mentioned it but if it weren't for two facts.

First, a couple weeks ago when I went to open the car, it wouldn't open via keyfob and I had to open the door via the metal key. The alarm had turned itself off so it was like the battery was dead. However when I turned the engine on, things started working and the car has been fine ever since.

Second, when I looked at the service records of the car I saw that the batteries had been changed multiple times before I got the car as follows: a) one battery was changed in 1/1/2012, b) both batteries were changed in 2/30/2019, c) Service battery was changed in 7/23/2019.

I've been monitoring both batteries for the last couple of weeks, and the front one is stable at 12V, the service one starts to slowly drop if the car is not driven for a few days. So this morning it was at 11.4V.

Before my car went dead I had the below error which when cleared would come back, however for about a week now the error has not been back.

B1 013-001 Terminal 1 5: Short circuit to battery.

Am I been paranoid and should just 'not fix it' until and if something actually stops working or should I try to diagnose something?

 

Intuitively, since terminal 15 is switched to 12 VDC by the ignition, if it is shorted to the battery it will cause the battery to discharge with the engine off. You might want to investigate by monitoring the current drawn on the battery as you sequentially remove and replace each fuse, or you can detect a circuit that isn't shutting down by measuring the voltage drop across its fuse. I'm not sure what voltage level you would look for, but you can get an idea through trial and error. (Measure the drop across a fuse which you know is conduction current. It will vary depending upon the fuse rating with higher-rated fuses drawing more current.)

Here are the electrical wiring diagrams if you need them: R230 ETM 64.

 

Your battery voltage is likely dropping fairly quickly because some circuit in your SL550 is drawing too much current from the consumer battery when the car is sitting in the garage or driveway. My new (to me) SL600 has a steady state current draw/drain of 160 milliamps (.16 amps) about 10 minutes after I shut it down; that is a HIGH current draw that even a 2 month old consumer battery in my car cannot handle very well. This level of current drain will result in a consumer battery low voltage warning in a day or so in my car and will likely damage any consumer battery over a relatively short period of time. For comparison, my 2006 Jeep Grand Cherokee has a much more normal 30 milliamp current draw less than 1 minute after shut down, from its single battery system. Yes, the R230 cars are far more complex than my V8 Jeep, but come on...

It is interesting that the MB engineers likely knew of high current draw problems long ago, or they probably would not have gone to the extra expense of having two separate batteries (starting and consumer), wiring, and control circuits to prevent stranding their vehicle owners. Rather than designing lower current draw alarm and sensor circuits so that their vehicles could be parked for long periods of time in parking garages, at airports or on the street, they opted for a more expensive and more complicated two battery solution. Can anyone explain this unusual design decision?

Pending troubleshooting of the high parked current draw of my SL600, I've had to add a consumer battery cutoff switch to my trunk-mounted consumer battery. The other option is to keep an AC powered trickle charger on it, but that doesn't work too well for road trips. Can others chime in with their steady state current draw numbers after their cars have been shut down for 5-10 minutes or so and various monitoring and sensor circuits should have shut themselves down?

 

A few months back Rodney explained that there are two batteries to ensure that the electric SBC braking system is always adequately powered.

A proper measurement of idle current draw requires that you wait for a period of time. I don't know what that interval is, but it may be 30 minutes or longer due to COMAND not always shutting down immediately.

 

The 14V is not your battery voltage when you start the car, this is the voltage regulator from the alternator that you are reading and should remain stable at 14V regardless of turning lights on or heater etc.
If your battery is 11.6V its very low, however it may be able to start the car, if you charge it on a long journey or battery charger it should get to around 12.6V but you need to turn the engine off to read the voltage remember otherwise you will just see 14.1VDC

 

If I understand what you are saying, the procedure is to either measure the change in battery voltage as I remove each fuse, so a 'problematic' circuit would still draw power with the fuse off. Or alternatively, switch the engine off and see which fuses drawn power and then determine if these fuses should not be drawing power?

Edit: Ignore my above. I did a bit more research and understand what I need to do to test the potential parasitic draw. Thank you for suggesting it. The only question I have is how does the car fully go to sleep? I'll leave the keyfob far and open with the metal key but opening the trunk and door will wake up the car. Wedging something on the door is easy enough to simulate door closure but how about the trunk and light in the trunk? And anything else I need to do to 'trick' the car that it should go to sleep?

 

Had similar problems. IF the PSE air pump is not working properly and doesnt close the trunk properly [sets trigger in CAN bus], THEN also the hydraulics of the cabrio roof will not work [although hydraulics are fine]. Replaced the PSE with revised part, and works flawlessly now! The SL500 was a very advanced machine in its time, so we have to diagnose/learn ...

 

If you open the trunk lid and examine its latch you may notice there is a rotary catch. If you rotate it part way with your finger or a tool the PSE will be triggered to rotate it fully just as if you had pushed the lid down to its closed position. With the catch in the locked position the rear SAM will regard the trunk lid as being closed.

 

Thank you, I'll do that.