SL/R230: Battery Warning Light (2008 MB SL 65 AMG)
02-18-2018, 10:11 AM
#1
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2008 MB SL65AMG
Battery Warning Light (2008 MB SL 65 AMG)
The red warning light comes up every time I start the vehicle. The 2 batteries are new and alternator is ok. I am afraid to drive the vehicle.
02-18-2018, 01:55 PM
#2
MBworld Guru
Just because the consumer battery is new and the alternator is working does not mean something isn't draining it. Note that the alternator doesn't really supply enough amps to "recharge" a drained battery - it's really just meant to maintain it and trickle-charge it. If you battery is getting drained overnight, then you need to diagnose what is causing that. If it takes several days sitting for the battery to drain down, then that is "normal" and you might want to invest in a C-Tek trickle charger.
02-18-2018, 04:54 PM
#3
Banned
If the alternator is outputting at least 13 volts with the engine idling, then I would not fear driving the car. If you have more than 13 volts on both batteries, then I would troubleshoot the fault indication by reading codes from the vehicle power systems module (N82) using a Star Diagnosis computer.
02-18-2018, 08:40 PM
#4
MBworld Guru
^^^ Ditto.
One thing I've noticed in diagnosing various voltage-related issues on MBZ cars is that the regulator takes "a minute" to start putting out voltage. I have had the red battery light on my SL once or twice even after installing a new battery (and alternator, last year). It only happens after I've sat int he car with the engine off, but listening to the radio, etc. I figure that using those consumers lowers the battery voltage just enough, and the regulator takes just enough time to start outputting that it trips the warning. I've pulled codes and get nothing. And of course if I stop the engine and check voltage during reest, cranking, and idle, it's then fine.
One thing I've noticed in diagnosing various voltage-related issues on MBZ cars is that the regulator takes "a minute" to start putting out voltage. I have had the red battery light on my SL once or twice even after installing a new battery (and alternator, last year). It only happens after I've sat int he car with the engine off, but listening to the radio, etc. I figure that using those consumers lowers the battery voltage just enough, and the regulator takes just enough time to start outputting that it trips the warning. I've pulled codes and get nothing. And of course if I stop the engine and check voltage during reest, cranking, and idle, it's then fine.
