SL/R230: Battery Problems
10-18-2012, 01:17 PM
#1
Battery Problems
I have a 2007 SL500. Two days ago I got a red message where the speedometer is. It showed a picture of the battery and it said take to workshop.
Today I used my code reader and there weren't any codes stored. When I started the car the rear battery was reading 13.89 volts so that meant the alternator was charging the battery, but after a minute or so the voltage dropped to 12.24 and kept dropping from there for about 45 seconds until the voltage reading leveled off at 11.95. I then shut off the engine and the voltage jumped back to 12.24. From there I did a load test and the needle stayed in the middle of the good range for the 10 second test.
I then checked the front battery and got a reading of 13.78 with the engine running and it held that voltage for a couple of minutes. From there I checked the battery with the engine off and got a voltage reading of 12.83. Then I put the load tester on the battery and the needle went just barely into the weak zone after about three or four seconds and stayed at that reading for the remainder of the 10 seconds.
One thing that seems certain is that the alternator quits feeding the rear battery after a minute or two while the engine is running and I say that because it seems like the alternator shouldn't drop down to a steady 11.95 if the battery voltage is that low.
Anybody have any suggestions or experiences that may help me?
Thanks.
Today I used my code reader and there weren't any codes stored. When I started the car the rear battery was reading 13.89 volts so that meant the alternator was charging the battery, but after a minute or so the voltage dropped to 12.24 and kept dropping from there for about 45 seconds until the voltage reading leveled off at 11.95. I then shut off the engine and the voltage jumped back to 12.24. From there I did a load test and the needle stayed in the middle of the good range for the 10 second test.
I then checked the front battery and got a reading of 13.78 with the engine running and it held that voltage for a couple of minutes. From there I checked the battery with the engine off and got a voltage reading of 12.83. Then I put the load tester on the battery and the needle went just barely into the weak zone after about three or four seconds and stayed at that reading for the remainder of the 10 seconds.
One thing that seems certain is that the alternator quits feeding the rear battery after a minute or two while the engine is running and I say that because it seems like the alternator shouldn't drop down to a steady 11.95 if the battery voltage is that low.
Anybody have any suggestions or experiences that may help me?
Thanks.
10-19-2012, 11:29 PM
#3
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e500
I have a 2007 SL500. Two days ago I got a red message where the speedometer is. It showed a picture of the battery and it said take to workshop.
Today I used my code reader and there weren't any codes stored. When I started the car the rear battery was reading 13.89 volts so that meant the alternator was charging the battery, but after a minute or so the voltage dropped to 12.24 and kept dropping from there for about 45 seconds until the voltage reading leveled off at 11.95. I then shut off the engine and the voltage jumped back to 12.24. From there I did a load test and the needle stayed in the middle of the good range for the 10 second test.
I then checked the front battery and got a reading of 13.78 with the engine running and it held that voltage for a couple of minutes. From there I checked the battery with the engine off and got a voltage reading of 12.83. Then I put the load tester on the battery and the needle went just barely into the weak zone after about three or four seconds and stayed at that reading for the remainder of the 10 seconds.
One thing that seems certain is that the alternator quits feeding the rear battery after a minute or two while the engine is running and I say that because it seems like the alternator shouldn't drop down to a steady 11.95 if the battery voltage is that low.
Anybody have any suggestions or experiences that may help me?
Thanks.
Today I used my code reader and there weren't any codes stored. When I started the car the rear battery was reading 13.89 volts so that meant the alternator was charging the battery, but after a minute or so the voltage dropped to 12.24 and kept dropping from there for about 45 seconds until the voltage reading leveled off at 11.95. I then shut off the engine and the voltage jumped back to 12.24. From there I did a load test and the needle stayed in the middle of the good range for the 10 second test.
I then checked the front battery and got a reading of 13.78 with the engine running and it held that voltage for a couple of minutes. From there I checked the battery with the engine off and got a voltage reading of 12.83. Then I put the load tester on the battery and the needle went just barely into the weak zone after about three or four seconds and stayed at that reading for the remainder of the 10 seconds.
One thing that seems certain is that the alternator quits feeding the rear battery after a minute or two while the engine is running and I say that because it seems like the alternator shouldn't drop down to a steady 11.95 if the battery voltage is that low.
Anybody have any suggestions or experiences that may help me?
Thanks.
10-20-2012, 03:24 AM
#4
Super Member
It sounds like you have a failed alternator/regulator. With the engine running the voltage should read the regulated alternator output (13.8v to 14.2v) regardless of battery condition. I have replaced the rear battery twice in my SL600 and even with the bad battery the system voltage was fine with the engine running.
I had the identical symptoms described above on my S65 (a single battery system). The alternator had failed, replacing it solved the problem. The battery was fine even though the dealer technician said otherwise.
I had the identical symptoms described above on my S65 (a single battery system). The alternator had failed, replacing it solved the problem. The battery was fine even though the dealer technician said otherwise.
10-20-2012, 06:15 PM
#5
Oops, sorry I didn't get back to this thread sooner. Most other forums I've signed up with let me know if there's a reply to my threads, but I didn't get any from this forum.
I'm going to start by saying, disregard the testing data above. I did some more thorough tests this morning and I also replaced the front battery yesterday. Here are the results of the testing done this morning:
1) Before running any tests this morning I checked the rear and front battery voltages and came up with front battery voltage (new battery) of 12.85 and a rear battery voltage of 12.73.
2) Then I started the engine and the front battery voltage was 14.19, although it slowly variated between 14.16 and 14.23 volts while the engine was running. The rear voltage when the engine started went to 13.95.
3) Within a minute or so, with the engine still running, the rear voltage started slowly dropping from the 13.95 to 12.24 where it stabilized, yet the front voltage remained at 14.16 to 14.23.
4) When the battery symbol and visit workshop message came on during the testing the front battery voltage dropped to 13.25 and the rear battery remained at 12.24.
5) I shut off the engine a let the car sit for 20 minutes or so and then checked the battery voltages again and the front battery showed 12.85 and the rear voltage was at 12.57.
Because of the voltages when the engine was started it told me the alternator was working and even though the front voltage dropped to 13.25 when the battery message came up it still told me the alternator was putting out although it's voltage drop was kinda weird. And, as far as the lower voltage reading (13.95) at the rear battery when the car was started, and the alternator was charging, versus the front battery voltage of 14.18 to 14.24, I think the explanation for that is the length of the battery cable going to the rear battery.
As for the rear battery voltage dropping off before the battery message came on, I spoke to one of the Mercedes' techs and he said there is thing called the "Charge Control" in the battery circuits that tells the alternator to send all the alternator's charging voltage only to the battery circuit that has the problem, which is usually a low battery voltage reading at one of the two batteries. However, last time I had a weak battery I got a message saying, "Conveniences Unavailable"
I found out this morning there is a TBS and a SB about voltage regulators needing replacement and it applied to my SL500 as well as many more models that were built in the last seven or eight years. And, on most of the treads that this was brought up on the people with the regulator problem got their regulators changed for free.
I have a Mercedes' Shop Manual (WIS) on my computer that tells how to check the alternator and regulator, but it's like reading a Greek manual. Does anyone know how to test the regulator?
As for my testing this morning, has anyone had similar problems/experiences where they were able to get the problem/s fixed and/or do you have any ideas that may be helpful?
Thanks.
I'm going to start by saying, disregard the testing data above. I did some more thorough tests this morning and I also replaced the front battery yesterday. Here are the results of the testing done this morning:
1) Before running any tests this morning I checked the rear and front battery voltages and came up with front battery voltage (new battery) of 12.85 and a rear battery voltage of 12.73.
2) Then I started the engine and the front battery voltage was 14.19, although it slowly variated between 14.16 and 14.23 volts while the engine was running. The rear voltage when the engine started went to 13.95.
3) Within a minute or so, with the engine still running, the rear voltage started slowly dropping from the 13.95 to 12.24 where it stabilized, yet the front voltage remained at 14.16 to 14.23.
4) When the battery symbol and visit workshop message came on during the testing the front battery voltage dropped to 13.25 and the rear battery remained at 12.24.
5) I shut off the engine a let the car sit for 20 minutes or so and then checked the battery voltages again and the front battery showed 12.85 and the rear voltage was at 12.57.
Because of the voltages when the engine was started it told me the alternator was working and even though the front voltage dropped to 13.25 when the battery message came up it still told me the alternator was putting out although it's voltage drop was kinda weird. And, as far as the lower voltage reading (13.95) at the rear battery when the car was started, and the alternator was charging, versus the front battery voltage of 14.18 to 14.24, I think the explanation for that is the length of the battery cable going to the rear battery.
As for the rear battery voltage dropping off before the battery message came on, I spoke to one of the Mercedes' techs and he said there is thing called the "Charge Control" in the battery circuits that tells the alternator to send all the alternator's charging voltage only to the battery circuit that has the problem, which is usually a low battery voltage reading at one of the two batteries. However, last time I had a weak battery I got a message saying, "Conveniences Unavailable"
I found out this morning there is a TBS and a SB about voltage regulators needing replacement and it applied to my SL500 as well as many more models that were built in the last seven or eight years. And, on most of the treads that this was brought up on the people with the regulator problem got their regulators changed for free.
I have a Mercedes' Shop Manual (WIS) on my computer that tells how to check the alternator and regulator, but it's like reading a Greek manual. Does anyone know how to test the regulator?
As for my testing this morning, has anyone had similar problems/experiences where they were able to get the problem/s fixed and/or do you have any ideas that may be helpful?
Thanks.
Last edited by hooperdoski; 10-20-2012 at 06:46 PM. Reason: Fix Mistake
