SL/R230: BATTERY OR CHARGING SYSTEM FAULT
Thread Starter
Senior Member
Joined: Oct 2021
Posts: 493
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
BATTERY OR CHARGING SYSTEM FAULT
R-230 COLEAGUES:
My rear battery gets discharged pretty fast, and charging takes over 20 miles drive. I am trying to determine if I have a defective charging system or a bad battery (AGM two years old). I took the battery to O'really to be checked, and the salesman told me it was Ok. Now I am planning to charge that battery and see if my consumers will get active. If it activates the consumers, will await for a couple of days and test again.
Then will concentrate in the charging system if battery testing proves OK. My code readers (Creader elite and Foxwell NT540 elite) do not indicate faults in the charging system.
Does anyone know a sure way to determine where the issue is????
Thanks again for your wise feedback!
My rear battery gets discharged pretty fast, and charging takes over 20 miles drive. I am trying to determine if I have a defective charging system or a bad battery (AGM two years old). I took the battery to O'really to be checked, and the salesman told me it was Ok. Now I am planning to charge that battery and see if my consumers will get active. If it activates the consumers, will await for a couple of days and test again.
Then will concentrate in the charging system if battery testing proves OK. My code readers (Creader elite and Foxwell NT540 elite) do not indicate faults in the charging system.
Does anyone know a sure way to determine where the issue is????
Thanks again for your wise feedback!
Joined: Nov 2016
Posts: 7,847
Likes: 3,495
From: Maryland
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
How did the guy at O'Reilly's check the battery? I know when I took a battery back to Sam's Club, they put it on some kind of machine to stress test the battery. It took like 20 minutes.
(P.S., Thanks for not yelling!)
(P.S., Thanks for not yelling!)
Super Member
Joined: Sep 2018
Posts: 746
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From: Melbourne, Australia
2005 SL 500 R230
They seem to eat batteries pretty fast.
Do you lock it when it's parked away? The car needs to be locked to go into deep sleep. Leaving the car unlocked will drain the battery.
Do you lock it when it's parked away? The car needs to be locked to go into deep sleep. Leaving the car unlocked will drain the battery.
Thread Starter
Senior Member
Joined: Oct 2021
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
Tom, that is good to know...I tested the rear battery voltage with the engine running and the voltage was 13.8 VDC. The battery itself was 11 VDC. That to me this is an indication of the charging system to be OK. I am using a "smart" battery charger to charge the battery now. What I plan is once charged, leave disconnected for 24 hrs and check the voltage again. If maintains the charge, then it would be a draining issue......will try with the car locked this time! 
Drinks coffee with Hazelnut creamer......!
Drinks coffee with Hazelnut creamer......!
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Joined: Mar 2008
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From: Glasgow, Scotland, UK
SL 350 R230 (3.7L with AMG Speedshift autobox)
Hi there, couple of points from me.
- How long have you had the rear battery? (if more than 6 years consider a new one)
- Is your rear battery a genuine Mercedes battery? if not then you will tend to get issues. I can say from experience that batteries are NOT all the same, they may have the same stats on the side (cold cranking amps, current rating etc) however I promise you if you get a genuine Merc battery it will last and your car will love you back !
- If your message 'convenience function not available' shows and it takes more than 10 mins to go away, your battery is no good. You should be able to leave your car 3 weeks+ with no issues.
- To test your alternator and voltage regulator, plug in a volt meter in the cigarette socket, (if you have 'convenience function not available' message, your lighter has no power so plug in a multimeter elsewhere to watch your volts. If your car charging is behaving you'll see 13.9V with engine on, then turn on rear heater and lights, it will dip down a few volts then the voltage regulator will get the reading back to around 13.9V.
Super Member
Joined: Sep 2018
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From: Melbourne, Australia
2005 SL 500 R230
It does sound like you have a failing or low rear battery. A dodgy battery in this car will give you various errors, red battery icon etc. Best just to change it.
Remember if the starting battery gives up the ghost you can always jump start the car, from the front battery only, with a portable jump pack which most car people seem to have these days.
Remember if the starting battery gives up the ghost you can always jump start the car, from the front battery only, with a portable jump pack which most car people seem to have these days.
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Joined: May 2020
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From: North Carolina, USA
2004 SL500AMG, 2003 SL500 USA
Most any auto parts place like autozone will test your alternator and battery for free. The batteries plus guy said a good battery should show at least 13 volts at rest, without the engine running.
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Thread Starter
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Joined: Oct 2021
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
Guys, thanks for taking the time to ventilate the rear battery issues. Yesterday I charged the battery with my smart charger and after that the voltage was 12.6 DCV. I re-connected the battery, locked the car and let it sleep overnight. This morning I checked the battery voltage and was 11.5 DCV. As E1EK mentioned, he could leave the car 3 months and still the battery is charged. Perhaps I need to replace the battery (Duracell AGM) which is 1 year 7 months old! By the way, in an earlier post I mentioned the car with erratic behavior after a week with the battery disconnected and re-connected....I figured that the rear battery was severely discharged, so most functions supported by it, weren't working! Any suggestions for a good and lasting AGM battery.?
I also figured that even though the AGM batteries has little evaporative emissions, they do have some, and since the trunk is an enclosed space, if the battery is not properly vented to the outside, corrosive gasses go around the electronics and degrades the electrical conduction. For example, at one point when trying to lower my roof, it didn't go and had a message to close the trunk canopy, but it was closed....so figured something wrong with the microswitch. After removing the microswitch housing, saw that the connector leads were corroded, and the switch was working properly....so cleaned the corrosion, applied grease and back to normal!
I also figured that even though the AGM batteries has little evaporative emissions, they do have some, and since the trunk is an enclosed space, if the battery is not properly vented to the outside, corrosive gasses go around the electronics and degrades the electrical conduction. For example, at one point when trying to lower my roof, it didn't go and had a message to close the trunk canopy, but it was closed....so figured something wrong with the microswitch. After removing the microswitch housing, saw that the connector leads were corroded, and the switch was working properly....so cleaned the corrosion, applied grease and back to normal!
MBWorld Fanatic!
Joined: Mar 2008
Posts: 1,232
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From: Glasgow, Scotland, UK
SL 350 R230 (3.7L with AMG Speedshift autobox)
Guys, thanks for taking the time to ventilate the rear battery issues. Yesterday I charged the battery with my smart charger and after that the voltage was 12.6 DCV. I re-connected the battery, locked the car and let it sleep overnight. This morning I checked the battery voltage and was 11.5 DCV. As E1EK mentioned, he could leave the car 3 months and still the battery is charged. Perhaps I need to replace the battery (Duracell AGM) which is 1 year 7 months old! By the way, in an earlier post I mentioned the car with erratic behavior after a week with the battery disconnected and re-connected....I figured that the rear battery was severely discharged, so most functions supported by it, weren't working! Any suggestions for a good and lasting AGM battery.?
I also figured that even though the AGM batteries has little evaporative emissions, they do have some, and since the trunk is an enclosed space, if the battery is not properly vented to the outside, corrosive gasses go around the electronics and degrades the electrical conduction. For example, at one point when trying to lower my roof, it didn't go and had a message to close the trunk canopy, but it was closed....so figured something wrong with the microswitch. After removing the microswitch housing, saw that the connector leads were corroded, and the switch was working properly....so cleaned the corrosion, applied grease and back to normal!
I also figured that even though the AGM batteries has little evaporative emissions, they do have some, and since the trunk is an enclosed space, if the battery is not properly vented to the outside, corrosive gasses go around the electronics and degrades the electrical conduction. For example, at one point when trying to lower my roof, it didn't go and had a message to close the trunk canopy, but it was closed....so figured something wrong with the microswitch. After removing the microswitch housing, saw that the connector leads were corroded, and the switch was working properly....so cleaned the corrosion, applied grease and back to normal!
If you want a battery that you can leave your car for a month in the middle of the coldest winter without issues get the genuine product.
Senior Member
Joined: May 2020
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From: North Carolina, USA
2004 SL500AMG, 2003 SL500 USA
Your battery is shot. I would return it, and see what is the trade in price is under it's warranty. A vent tube is standard. A 90 degree elbow plugs into the top side wall of the positive terminal side of the battery. The attached tube is about 1/4" in diameter, and goes and vents through a hole in the trunk floor.
Super Member
Joined: Jul 2007
Posts: 742
Likes: 228
From: Santa Barbara, CA
S550C4, Porsche Cayenne
elMacko, I have heard from many SL owners and mechanics over the years that the best way to avoid problems is to use the MBZ battery. You don't really save a lot of $ by using a different brand. And these cars seem to be sensitive to other types of batteries. I have a 2005 SL and recently had similar low voltage issues as you report. Had a new (MBZ) battery installed and all is fine. Good luck.
Super Member
Joined: Aug 2017
Posts: 520
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From: Scottsdale AZ
2015 SL550 & 2012 S550 4matic
Endorse prior recommendations for OEM MB batteries. Bought my SL 5 years ago and it had OEM battery 8 years old, Ran it for 2 years before replacing it and 10 year old starter batteries with OEM, just for peace of mind, I was having no issues. Checked auto parts stores for price comparison and took it to dealer parts manager who provided a 10% discount to make the difference negligible. Go OEM you will be happy.
Senior Member
Joined: May 2020
Posts: 443
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From: North Carolina, USA
2004 SL500AMG, 2003 SL500 USA
WARNING: If you fully discharge a new battery several times, it may go bad and not hold a good charge. This can happen with a second/non-daily driver. It has something like an alarm that drains the battery. You charge the battery. It fully discharges repeatedly.
Thread Starter
Senior Member
Joined: Oct 2021
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
Gentlemen, after following Tom's suggestion, I have "locked" the vehicle for 48 hours and the battery (rear) have lost 1 volt (from fully charged). That is much less than the loss experienced when leaving the vehicle unlocked for the same period of time..! But today after 72 hrs the voltage was 9.5...!
I read on archives that the consuming power in sleep state is 20 Ma, that should be sufficient to keep the battery alive for at least a week! the problem is measuring that minimal amount on a thick cable..! I assume, I have to start removing suspicious fuses and watch the outcome!
Thank you for sharing that wealth of knowledge!
I read on archives that the consuming power in sleep state is 20 Ma, that should be sufficient to keep the battery alive for at least a week! the problem is measuring that minimal amount on a thick cable..! I assume, I have to start removing suspicious fuses and watch the outcome!
Thank you for sharing that wealth of knowledge!
Last edited by elMacko; Oct 24, 2023 at 06:07 PM.
Thread Starter
Senior Member
Joined: Oct 2021
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
E1EK, understand your point on the Mercedes battery........but, as you well know many car manufacturers do the same on many of aftermarket replacement components such as OIL, batteries, coolants, etc. The fact of the matter is that the manufacturer's of these components use the car manufacturer's demands to improve their product and have more sales in the aftermarket..! I will buy a Varta over the Mercedes brand without any reservation.
As an example, I used to work for a consumer product manufacturer who was making products for the Sears brand, Sears representatives conducted periodical visits and audits to make sure their product was as expected. On the other hand, that product with a different housing color was sold to other markets at slightly lower prices.! More volume>>>>less cost! But, sometimes as you said, there are not apples to apples, I used to own a motorcycle and used China made ignition modules that lasted only a year..! Changed it for the OEM, and lasted for ever..! The Mercedes logo in many parts makes them very expensive compared to Aftermarket....a shock is an example: Bilstein $120 Mercedes $240..! I know Mercedes uses Bilstein for their shocks!
As an example, I used to work for a consumer product manufacturer who was making products for the Sears brand, Sears representatives conducted periodical visits and audits to make sure their product was as expected. On the other hand, that product with a different housing color was sold to other markets at slightly lower prices.! More volume>>>>less cost! But, sometimes as you said, there are not apples to apples, I used to own a motorcycle and used China made ignition modules that lasted only a year..! Changed it for the OEM, and lasted for ever..! The Mercedes logo in many parts makes them very expensive compared to Aftermarket....a shock is an example: Bilstein $120 Mercedes $240..! I know Mercedes uses Bilstein for their shocks!
Super Member
Joined: Sep 2018
Posts: 746
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From: Melbourne, Australia
2005 SL 500 R230
The problem is measuring that minimal amount on a thick cable! I assume I have to start removing suspicious fuses and watch the outcome
You're flying blind unless you start measuring. You need a DC milliamp clamp meter, to see what's going on.
You could start by taking out the radio fuse and the siren fuse, both of those are known current eaters.
You're flying blind unless you start measuring. You need a DC milliamp clamp meter, to see what's going on.
You could start by taking out the radio fuse and the siren fuse, both of those are known current eaters.
Thread Starter
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Joined: Oct 2021
Posts: 493
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
Tom, I am trying to learn the functions on my Foxwell510, so far it indicated faults in the telephony system and the upper desk...try to print a report but couldn't retrieve the particulars.....will try again as soon as the wife leave me run free!
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Joined: Sep 2018
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From: Melbourne, Australia
2005 SL 500 R230
Yeah it takes a bit of running around. Play with it. You don't have to run a full scan each time - that takes ages - just go to control modules, then the section you want.
Also you sometimes have to try several times to clear a code. If you've fixed the fault and the code won't clear, try turning the car off for a bit and wait then on again. Scan again and keep trying to clear it, it's a bit buggy, or that may be the car's software.
First up, run a full scan and clear everything out, probably got lots of old redundant codes. Then full scan again, see what comes back.
It's a great little tool but I wouldn't bother trying to export data. Just take photos of codes that won't clear then look them up later.
Also you sometimes have to try several times to clear a code. If you've fixed the fault and the code won't clear, try turning the car off for a bit and wait then on again. Scan again and keep trying to clear it, it's a bit buggy, or that may be the car's software.
First up, run a full scan and clear everything out, probably got lots of old redundant codes. Then full scan again, see what comes back.
It's a great little tool but I wouldn't bother trying to export data. Just take photos of codes that won't clear then look them up later.
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Joined: Mar 2008
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From: Glasgow, Scotland, UK
SL 350 R230 (3.7L with AMG Speedshift autobox)
These are valid points you have mentioned in regards to manufacturers keeping costs down by re-using parts elsewhere. Mercedes are good at that, as many same component parts are used across their different models. However this is not always the case and for specialised components they will take more engineering expertise.
I have spent two decades as a Lean Black Belt and understand Six Sigma and manufacturing process well, but not bragging. You mentioned that you will buy Varta over Mercedes well Varta make the Mercedes battery for them as its written on the side of mine, it makes sense as you mentioned for Mercedes to utilise an already established battery supplier rather than create their own manufacturing plant. I worked for BMW on a project for an oil sensor for their 7 series as a senior engineer for Honeywell, BMW's quality checks were so intense that it got stupid, they absolutely would not let any defects through their process. In short BMW utilised Honeywell to manufacture their sensor and I believe that Mercedes QA criteria with Varta will be equally as stringent and although made by the same company, would not let any standard Varta battery do for the SL as it would have been specified and tested to the hilt.
I have spent two decades as a Lean Black Belt and understand Six Sigma and manufacturing process well, but not bragging. You mentioned that you will buy Varta over Mercedes well Varta make the Mercedes battery for them as its written on the side of mine, it makes sense as you mentioned for Mercedes to utilise an already established battery supplier rather than create their own manufacturing plant. I worked for BMW on a project for an oil sensor for their 7 series as a senior engineer for Honeywell, BMW's quality checks were so intense that it got stupid, they absolutely would not let any defects through their process. In short BMW utilised Honeywell to manufacture their sensor and I believe that Mercedes QA criteria with Varta will be equally as stringent and although made by the same company, would not let any standard Varta battery do for the SL as it would have been specified and tested to the hilt.
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Joined: Oct 2021
Posts: 493
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
My Scottish colleague,
Well understood what you said since I have been a facilitator for Six Sigma too..
But lets go beyond Lead Acid AGM. Now we have Lithium-Ion batteries 12V 50 and 80 ah packages that are lighter, more powerful and efficient than lead acid. . Lithium-Ion batteries behave an extremely small capacity loss while sitting unused. They will produce much more current in a given space. One of the benefits of Lithium batteries over AGM is that they charge faster. However, when the lithium battery has a voltage lower than its power supply, it will consume as much as it is possibly to make up for the difference in voltage. This can cause the alternator and cables to overheat. That is why to put some sort of current limiting device between the alternator and the Lithium battery. A DC to DC buck converter solves this issue.
So, figuring out the cost, a 12V, 100aH lithium battery sells for $200 US and the buck converter for $30 US, so $230 US and will last for near 10 years!!!
I wonder if anyone in the forum has done that!
Well understood what you said since I have been a facilitator for Six Sigma too..
But lets go beyond Lead Acid AGM. Now we have Lithium-Ion batteries 12V 50 and 80 ah packages that are lighter, more powerful and efficient than lead acid. . Lithium-Ion batteries behave an extremely small capacity loss while sitting unused. They will produce much more current in a given space. One of the benefits of Lithium batteries over AGM is that they charge faster. However, when the lithium battery has a voltage lower than its power supply, it will consume as much as it is possibly to make up for the difference in voltage. This can cause the alternator and cables to overheat. That is why to put some sort of current limiting device between the alternator and the Lithium battery. A DC to DC buck converter solves this issue.
So, figuring out the cost, a 12V, 100aH lithium battery sells for $200 US and the buck converter for $30 US, so $230 US and will last for near 10 years!!!
I wonder if anyone in the forum has done that!
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Senior Member
Joined: Oct 2021
Posts: 493
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From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
Guys, I removed the battery, fully charged it. Put a 10 amp Led bulb on it...the next morning was at 11 volts..>! Doing the math, that 80 Ah battery should have been capable of having that bulb running for 90 hrs!
Took the battery back to Sam's Club, no questions asked, they didn't even test it....just gave me a new one and thank you good by!
No discharging problems anymore.....! But will keep the car locked while not in use.
Thank you gentlemen for the good tips anyway!
Took the battery back to Sam's Club, no questions asked, they didn't even test it....just gave me a new one and thank you good by!
No discharging problems anymore.....! But will keep the car locked while not in use.
Thank you gentlemen for the good tips anyway!
