2013 GLK 4MATIC Alternator & charging circuitry
Thread Starter
Member
Joined: Oct 2020
Posts: 183
Likes: 41
From: Ottawa, Ontario
2013 GLK350 Canada
2013 GLK 4MATIC Alternator & charging circuitry
Does anyone have a schematic showing the alternator, main battery, secondary (trunk) battery, the charging circuitry, the control circuitry, and the location of any modules involved in charging? Looks like my alternator and both batteries are working ok, I need to check the charging circuitry (wiring). Any guidance, or knowledge of usual failure points would be appreciated.
Many thanks!
Steve
Many thanks!
Steve
Thread Starter
Member
Joined: Oct 2020
Posts: 183
Likes: 41
From: Ottawa, Ontario
2013 GLK350 Canada
I've been chasing the elusive red battery warning solution. Don't have much hair left to pull out, ha ha
. I've posted here a couple of times about it, but still haven't found a solution.
I did a little more digging. I searched forums for threads containing "alternator" and found this excellent discussion about (and description of) the dual battery system and its' testing way down the page of search results. It gives a great idea of the circuitry, how it works, how the Auxilliary battery is used, and how to test.
Not sure how to link to other posts or their authors, so here are the links (and names) I copied....
Posted in the SL-Class (R230) forum by mrvedit within the posting "Red battery warning".
https://mbworld.org/forums/attachments/sl-class-r230-17/electrical-issue-consumer-battery-wont-charge-532919/r230-dual-battery-system-425370d1591305151
Here's the link to the full post:
https://mbworld.org/forums/sl-class-...y-warning.html
Mant thanks to:
@wireless
@aegea
@mrvedit
for their excellent contributions.
Now to isolate the problem part.
Best,
Steve
. I've posted here a couple of times about it, but still haven't found a solution.I did a little more digging. I searched forums for threads containing "alternator" and found this excellent discussion about (and description of) the dual battery system and its' testing way down the page of search results. It gives a great idea of the circuitry, how it works, how the Auxilliary battery is used, and how to test.
Not sure how to link to other posts or their authors, so here are the links (and names) I copied....
Posted in the SL-Class (R230) forum by mrvedit within the posting "Red battery warning".
https://mbworld.org/forums/attachments/sl-class-r230-17/electrical-issue-consumer-battery-wont-charge-532919/r230-dual-battery-system-425370d1591305151
Here's the link to the full post:
https://mbworld.org/forums/sl-class-...y-warning.html
Mant thanks to:
@wireless
@aegea
@mrvedit
for their excellent contributions.
Now to isolate the problem part.
Best,
Steve
Last edited by KanataSteve; Jan 25, 2026 at 06:53 PM. Reason: Incorrect link
MBWorld Fanatic!
Joined: Sep 2015
Posts: 2,585
Likes: 343
2013 glk 350
You said it’s charging , battery is good at maybe 12.7 after rest . It starts , It charges when running at 14-14.7 ? You have had it scanned, you had battery and alternator tested. Maybe there is no problem. Just some bad sensor setting off a bs warning . Did you check phantom load loss ? Black electric tape can make the warning light go away.
Thread Starter
Member
Joined: Oct 2020
Posts: 183
Likes: 41
From: Ottawa, Ontario
2013 GLK350 Canada
Funny thing is that is only shows a problem below -10°C. The voltage/current display only indicates a dropping voltage and negative current at that time. When the temp is closer to zero, it behaves normally.
I just saw an Aux Battery warning this evening, so now I'm wondering if it's really the Aux battery or the control module.
The other curious thing is that the display indicates charging up to 15 Volts (with a reducing current down to about 1.6 Amps as it gets to 15V). I thought that charging voltage was limited to 14.7?
I just saw an Aux Battery warning this evening, so now I'm wondering if it's really the Aux battery or the control module.
The other curious thing is that the display indicates charging up to 15 Volts (with a reducing current down to about 1.6 Amps as it gets to 15V). I thought that charging voltage was limited to 14.7?
MBWorld Fanatic!
Joined: Sep 2015
Posts: 2,585
Likes: 343
2013 glk 350
I think on your last thread I mentioned the alternator regulator. Mine went bad at 80,000, a good one is about 100$ and an hour to put in. I tried watching the v meter in the engineer
menu and it was crazy watching the up down movement. Today I just installed a Ancel bm 200, it’s a 27$ monitor that might help , I think it has a Diode tester which should be the regulator! And I just got a Ancel BA 101. 50$ battery tester that tests everything. Project Farm on YouTube just revived a lot of battery testers. Test both batteries and charge the auxiliary. I bought a 50-60$ replacement off Amazon
menu and it was crazy watching the up down movement. Today I just installed a Ancel bm 200, it’s a 27$ monitor that might help , I think it has a Diode tester which should be the regulator! And I just got a Ancel BA 101. 50$ battery tester that tests everything. Project Farm on YouTube just revived a lot of battery testers. Test both batteries and charge the auxiliary. I bought a 50-60$ replacement off Amazon
Last edited by Mmr1; Jan 25, 2026 at 08:24 PM.
