SL/R230: STARTER BATTERY NOT CHARGING
Junior Member
Joined: Dec 2015
Posts: 64
Likes: 4
From: Los Angeles , Ca
2011 S63 , 1997 SL500 La costa edition (sold) 1987 560SEC (sold)
vin # WDDNG7EBXBA372226
If I may ask you a huge favor while you're at , I need to replace the serpentine belt (belt drive) and I couldn't find any right up on it, if you can post the PDF I would really appreciate it
Junior Member
Joined: Dec 2015
Posts: 64
Likes: 4
From: Los Angeles , Ca
2011 S63 , 1997 SL500 La costa edition (sold) 1987 560SEC (sold)
Hello again and thank for your help the last time, I'm facing another issue and I posted a request in the forum but no buddy responded so I thought I'll reach out to you again , I need to replace a thermostat and it's not very easy to do on the 157 engine if I can bother you again and get the PDF on it, I would really appreciate it, you have my vin in the above post thanks in advance
Member
Joined: Jun 2024
Posts: 121
Likes: 0
SL55 amg R230
Hi i have put some new prefuses in because of corrosion i was tracing a no crank no start issue and after changing the fuses the starter battery has no power at all any advice please?
i had both batteries disconnected
i had both batteries disconnected
Thread Starter
Senior Member
Joined: Oct 2021
Posts: 493
Likes: 101
From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
Does the starter turns the engine with batteries fully charged? If not, Are the batteries fully charged? If the engine turns, then check the Crankshaft position sensor! Is fuel getting into the cylinders? Fuel filter clogged? Are the any sparks? There are many tests to do to determine the root cause by eliminating obvious causes..!
Member
Joined: Jun 2024
Posts: 121
Likes: 0
SL55 amg R230
Does the starter turns the engine with batteries fully charged? If not, Are the batteries fully charged? If the engine turns, then check the Crankshaft position sensor! Is fuel getting into the cylinders? Fuel filter clogged? Are the any sparks? There are many tests to do to determine the root cause by eliminating obvious causes..!
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Senior Member
Joined: Nov 2021
Posts: 469
Likes: 119
From: North West England
SL500
What do you mean by the starter battery has no power?
Have you measured battery voltage, and drop load voltage/amps?
Consumer battery is needed to power up all the modules so a bad consumer battery can cause no cranking, but if the rear battery is only discharged slightly, then the BCM would bridge the two batteries together to enable starting.
Have you measured battery voltage, and drop load voltage/amps?
Consumer battery is needed to power up all the modules so a bad consumer battery can cause no cranking, but if the rear battery is only discharged slightly, then the BCM would bridge the two batteries together to enable starting.
Thread Starter
Senior Member
Joined: Oct 2021
Posts: 493
Likes: 101
From: Benton, Louisiana, USA
SL 500 2004, Ford F-150-2014
gOrsq, I do not think that the "consumers" battery could start the engine if the starter battery is depleted...! Figure the amps needed to be handle by K57...! And the BCM has no power circuits to allow heavy loads through! If a little boost is needed, I can believe that, but essentially most of the juice has to come from the starter battery!
Also see the Gauge of the wires connecting the BCM with the starter battery....not sufficient to handle the starter motor amps..!
Also see the Gauge of the wires connecting the BCM with the starter battery....not sufficient to handle the starter motor amps..!
Senior Member
Joined: Nov 2021
Posts: 469
Likes: 119
From: North West England
SL500
Who said it would?
I said the STARTER battery would be used to boost the consumer battery, so the essential systems could function, including the ignition and starter systems, and hence enable the car to start.
The relay and cabling would still need to carry a high current, but only for a very short time.
I don't think the system is functional the other way, but I don't know.
On a side point, have you seen the small jumper packs, which can be used to start a car with a flat battery. They only have small terminals and cables!
This is because a battery that can not start a car still has a lot of power in it. It's just the voltage which is too low to move the amps.
The jump packs just boost the battery voltage by adding enough current to get the voltage high enough to crank the engine. On their own the can't start a car, they still need the power remaining in the low battery.
I said the STARTER battery would be used to boost the consumer battery, so the essential systems could function, including the ignition and starter systems, and hence enable the car to start.
The relay and cabling would still need to carry a high current, but only for a very short time.
I don't think the system is functional the other way, but I don't know.
On a side point, have you seen the small jumper packs, which can be used to start a car with a flat battery. They only have small terminals and cables!
This is because a battery that can not start a car still has a lot of power in it. It's just the voltage which is too low to move the amps.
The jump packs just boost the battery voltage by adding enough current to get the voltage high enough to crank the engine. On their own the can't start a car, they still need the power remaining in the low battery.
Newbie
Joined: Feb 2026
Posts: 1
Likes: 0
Great to find this thread which shows where the big Alternator fuses are.
I've had battery drain issues ever since I bought my 2004 SL600 in late 2021; the dealer even installed a new rear (Consumer) battery in it before I bought it. I really needed to drive the car at least once a week, or it wouldn't start.
As expected after storing the car for two winter months in a trailer with no trickle chargers, both batteries were dead; especially the rear battery which read only 2V. We jumped the car, left it running and drove it for an hour, but the rear battery would no longer hold a charge; its ruined. (Not even after overnight on a 4 AMP charger.)
I therefore decided to chase down the drain. After everything settled down (about 10 minutes), it was still draining 210mA, enough to drain a battery in 2 weeks. I started by removing the 20AMP PSE fuse, but no improvement. I then went through all 78 fuses in the 3 fuse boxes. Removing 20 at a time and waiting 10 minutes, made no difference, still 210mA (.21 Amps).
Until I just found this post, I couldn't find if/where the Alternator was fused. (Some cars use a fuseable link wire.)
So GREAT to find this post.. Next test is to check if the alternator is draining the battery by removing those big fuses. I've read here that it is common for the Alternator's "voltage regulator" to degrade and drain the battery.
Am I correct that this "voltage regulator" is part of the Alternator and to replace it the Alternator needs to be removed?
In the meantime, I just bought an AGM H6 battery from Autozone as I don't want to deal with the MB dealer.
For those curious, the AutoZone Duralast Platinum H6-AGM battery fits perfectly, cost $240 and has a 3 year full replacement warranty.
Note that I have read that some R230 SL may have the bigger H8 battery in the rear, but mine was definitely H6 sized and was MB part # A001-982-80-08. It is 11 inches long.
I've had battery drain issues ever since I bought my 2004 SL600 in late 2021; the dealer even installed a new rear (Consumer) battery in it before I bought it. I really needed to drive the car at least once a week, or it wouldn't start.
As expected after storing the car for two winter months in a trailer with no trickle chargers, both batteries were dead; especially the rear battery which read only 2V. We jumped the car, left it running and drove it for an hour, but the rear battery would no longer hold a charge; its ruined. (Not even after overnight on a 4 AMP charger.)
I therefore decided to chase down the drain. After everything settled down (about 10 minutes), it was still draining 210mA, enough to drain a battery in 2 weeks. I started by removing the 20AMP PSE fuse, but no improvement. I then went through all 78 fuses in the 3 fuse boxes. Removing 20 at a time and waiting 10 minutes, made no difference, still 210mA (.21 Amps).
Until I just found this post, I couldn't find if/where the Alternator was fused. (Some cars use a fuseable link wire.)
So GREAT to find this post.. Next test is to check if the alternator is draining the battery by removing those big fuses. I've read here that it is common for the Alternator's "voltage regulator" to degrade and drain the battery.
Am I correct that this "voltage regulator" is part of the Alternator and to replace it the Alternator needs to be removed?
In the meantime, I just bought an AGM H6 battery from Autozone as I don't want to deal with the MB dealer.
For those curious, the AutoZone Duralast Platinum H6-AGM battery fits perfectly, cost $240 and has a 3 year full replacement warranty.
Note that I have read that some R230 SL may have the bigger H8 battery in the rear, but mine was definitely H6 sized and was MB part # A001-982-80-08. It is 11 inches long.
does your car throw that red battery warning light?
if yes, try checking your BCM, theres probably a power leakage that drains your battery overnight. Have it inspected & tested by a professional electrician. Hence once u solve that, you are happy as you go.
p/s new bcm costs you thousands.. i recommend you to send it to a professional electrician
Last edited by BB500SLmaster; Feb 6, 2026 at 12:05 AM.
Super Member
Joined: Sep 2021
Posts: 534
Likes: 115
From: Ann Arbor, MI
2004 SL600
did you manage to solve your problem?
does your car throw that red battery warning light?
if yes, try checking your BCM, theres probably a power leakage that drains your battery overnight. Have it inspected & tested by a professional electrician. Hence once u solve that, you are happy as you go.
p/s new bcm costs you thousands.. i recommend you to send it to a professional electrician
does your car throw that red battery warning light?
if yes, try checking your BCM, theres probably a power leakage that drains your battery overnight. Have it inspected & tested by a professional electrician. Hence once u solve that, you are happy as you go.
p/s new bcm costs you thousands.. i recommend you to send it to a professional electrician
Like many others have noticed, these cars have significant parasitic draw which will drain the rear battery within a month for most.
My parasitic draw is around 130 mA which is higher than some others but in line with many. Seems nearly everyone has to put a battery tender on the rear battery if the car isn't driven bi-weekly.
I have tried a few times to chase down the draw, most recently using the PowerProbe PPDRAW parasitic drain monitor. and PPFUSE fuse monitor.
I plan to document when I'm done with my testing, but in the meantime:
BCM - Since mine is now fused as all should be, easy to disconnect = 0mA
Alternator - Disconnect makes no change =0mA
Engine Fan - Easy to disconnect; make no change =0mA
SBC - Easy to disconnect, but obviously needed and not easy to swap =25mA
Front Left Fuse Box - Best estimate for sum of all fuses (With Alarm fuse pulled) =10mA
Front Right Fuse Box - Best estimate for sum of all fuses, not including SBC =10mA
Little green light in trunk which seems to stay on =10mA
So about 80mA is still unaccounted for. I suspect it is related to the rear passenger side fuse box, but it is very hard to reach probes onto individual fuses. When I do complete that I will document it all.
In the meantime I keep a battery tender on the rear battery as much as possible.
