SL/R230: Starter battery charge??? Stuck now?
Thread Starter
Newbie
Joined: May 2018
Posts: 2
Likes: 0
From: Lincolnshire, uk
R230 sl500
Starter battery charge??? Stuck now?
Okay guys I have a r230 sl500 at 79kml and I'm stuck I have a red battery warning light with brand new front and rear battery, never get consumer electric warning and all electrics work as it should, my alternator and regulator work fine as when engine is running my rear battery is charging at 14.5v (tested with multi meter) but my starter battery is recieveing no charger at all (11.8v engine running) all fuses are okay checked the pre fuses in passenger footwell all fine, why is my starter battery not receiving any charge is it my BCM? Live data also shows terminal 30 at 0v and this never changes?! I'm stuck guys.
Banned
Joined: Jan 2006
Posts: 1,982
Likes: 393
From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
I'd presume the power supply controller ("BCM") is bad. The following test would provide some confirmation.
Disconnect the rear battery. Insert the ignition key and turn it to position 2. For c. 30 seconds you should have electrical power to most electrical consumers, and you can even start the car. If that is not the case, then the power supply controller is bad.
Disconnect the rear battery. Insert the ignition key and turn it to position 2. For c. 30 seconds you should have electrical power to most electrical consumers, and you can even start the car. If that is not the case, then the power supply controller is bad.
Thread Starter
Newbie
Joined: May 2018
Posts: 2
Likes: 0
From: Lincolnshire, uk
R230 sl500
Both batteries engine off show 12.5v just front battery connected I get consumer electrics and car will start and front charging but battery light on then with both batteries connected I have all electrics back, boot battery charging 14.1v front charging all over the place 14.3, 14.5, 14.8, 14.7 and will fluctuate between those voltages quite rapidly but still battery warning light. After about a day the rear will always charge at 14.1 but the front will drop to 13.5-6 and will not charge higher than that and will always have battery warning light when strickig up.
Senior Member
Joined: Jan 2015
Posts: 389
Likes: 113
From: Seattle, WA
SL500
Shot in the dark here, but since I've seen this happen with a motorcycle battery, I'll put it out there just in case. Often servicable batteries are sold without electrolyte. They're supposed to come with electrolyte to be mixed in at point of sale. Since the starter battery is not a sealed unit, might want to have a look at the electrolyte levels.
