Visit workshop with battery sign every time after diving 20km

[Ozzy350]

Hi there,
I have a 2004 SL350. I removed the main battery in order to charge at night (level was low after longtime no use), but left the starter connected (obviously a mistake because drained that one too overnight). So the next day I charged the stater battery as well. After properly connected the both batteries (first starter and then the main), everything was fine until the first 20km, then this famous red visit workshop warning comes up. It disappears when vehicle sleeps about 5-10min, but comes back again after 20-30km driving. I’ll appreciate if someone can help me to erase this message which is very annoying. The car works fine, alternator charges good. Thank you very much

 

[Uncle Benz]

I’ve had a few headaches with these over the years. They have a complex battery system I’ve never found easy to diagnose. There is a battery distribution module in the boot that I have changed more of than alternators, although I’ve done a few alternators too. I keep a new battery control module on the shelf (don’t ask! It’s nearly £400 worth). Substitution is the only sure test I’ve found for it. You are welcome to borrow it to try if nearby.

 

[Ozzy350]

I’ve had a few headaches with these over the years. They have a complex battery system I’ve never found easy to diagnose. There is a battery distribution module in the boot that I have changed more of than alternators, although I’ve done a few alternators too. I keep a new battery control module on the shelf (don’t ask! It’s nearly £400 worth). Substitution is the only sure test I’ve found for it. You are welcome to borrow it to try if nearby.

thank you so much for your generous offer for help, but I’m in France so it will not be possible. I’ve just disconnected again both batteries and waited around 30min before connecting (first starter and then main) as suggested in some posts. I’ll drive tomorrow to see if it works. I’ve searched for this battery control module in the boot, but I can not locate it. Is it the black module with 7A fuse on it? Because it doesn’t look like the metallic box as I see at Internet. I’ll also call my repair shop to ask if can somehow erase this message. I’ll keep updated if I manage to figure it out

 

[Uncle Benz]

It’s under the carpet liner just above, to the right and slightly further into the car than the battery

 

[Ozzy350]

Thanks!
For information, disconnecting neg poles, waiting 25mn and reconnecting didn’t work. Same message after exactly 28km. I’ll run the battery and alternator test again today and trying to get an appointment at workshop to run a diag and try to erase it (hopefully).