Battery and Alternator Question for CLK500
12-10-2017, 02:13 PM
#1
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Battery and Alternator Question for CLK500
A few days ago I tried to cold start my 2004 CLK500 but I couldn't due to a dead battery which was strange since I drove the car the night before and it had no issues starting. I enabled Dyno Mode so I can see the voltage and I saw that my battery was at 8 volts (it was a Duralast Platinum AGM battery that was installed exactly a year ago)! At that point I suspected that 2 of the battery cells failed but I attempted to recharge it overnight anyway, but it never went above 8V. After checking online regarding Duralast AGM Batteries (low quality, bad reviews), I bought a Bosch AGM battery as a replacement and installed it.
It appears the battery was the cause of problems, but I don't want to discount other possibilities like the alternator and/or overnight parasitic draw. Regarding the alternator, it's the original and has 115K miles on it (with only 25K miles on the Voltage Regulator), When I cold start the car with the new battery, the voltage starts at 14.2V, then idles at 14V. After 5 minutes, the voltage trickles down to 13.8 then eventually it goes to 13.5V at Idle (no accessories running) after another 5 minutes. I've heard that with fully charge new batteries, since it doesn't need to charge much, the alternator will go as low as 13.5V after a short while.
As for the parasitic draw, I'm planning on doing the Current Draw test procedure where I run the mutimeter in series with the battery, set the mutimeter to Amps, wait till the car sleeps (after 30 minutes after power off), check the amperage draw (should be less than 0.1A) and start pulling fuses (and watch the amperage drop) to see what is drawing the most power (like the Seat Modules or shorted Dome Light Panel). With the new battery, after leaving the car over night, the voltage is at 12.7V when I start in the morning.
With all this info, I wanted to see what the MBworld community thinks of my situation. It could just been a bad battery all along, maybe there is something drawing a lot of power over night; if the alternator is on the way out, I can replace it, but I wanted some opinions on it before I spend $350.
It appears the battery was the cause of problems, but I don't want to discount other possibilities like the alternator and/or overnight parasitic draw. Regarding the alternator, it's the original and has 115K miles on it (with only 25K miles on the Voltage Regulator), When I cold start the car with the new battery, the voltage starts at 14.2V, then idles at 14V. After 5 minutes, the voltage trickles down to 13.8 then eventually it goes to 13.5V at Idle (no accessories running) after another 5 minutes. I've heard that with fully charge new batteries, since it doesn't need to charge much, the alternator will go as low as 13.5V after a short while.
As for the parasitic draw, I'm planning on doing the Current Draw test procedure where I run the mutimeter in series with the battery, set the mutimeter to Amps, wait till the car sleeps (after 30 minutes after power off), check the amperage draw (should be less than 0.1A) and start pulling fuses (and watch the amperage drop) to see what is drawing the most power (like the Seat Modules or shorted Dome Light Panel). With the new battery, after leaving the car over night, the voltage is at 12.7V when I start in the morning.
With all this info, I wanted to see what the MBworld community thinks of my situation. It could just been a bad battery all along, maybe there is something drawing a lot of power over night; if the alternator is on the way out, I can replace it, but I wanted some opinions on it before I spend $350.
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CaliBenzDriver (03-17-2021)
12-10-2017, 10:55 PM
#4
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Thats the answer I was hoping for; if I had a big parasitic draw, I figure the the voltage would be lower.
02-14-2018, 07:25 PM
#5
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Mercedes CLK 320 2005
Activating this thread.
I seem to be have the same problem. 2005 CLK 320, car wouldn't start. Jumped it and drove it to Autozone and got a new battery. Battery worked for 36 hours then I couldn't start the car again (no lights, key remove doesn't work, radio doesn't turn on).
What is dyno mode and how do I activate it? Should I get a multimeter and do what you are doing? Did you figure out what happened to your car?
I seem to be have the same problem. 2005 CLK 320, car wouldn't start. Jumped it and drove it to Autozone and got a new battery. Battery worked for 36 hours then I couldn't start the car again (no lights, key remove doesn't work, radio doesn't turn on).
What is dyno mode and how do I activate it? Should I get a multimeter and do what you are doing? Did you figure out what happened to your car?
02-14-2018, 10:09 PM
#6
MBworld Guru
I would just get a multimeter. But if you want dyno mode for the onboard voltmeter do this: turn the key to position 1 ("accessory"). Use the steering wheel controls to select the default menu on the MFD, This will show either the outside temperature or 0mph, depending on your personal settings. Press the reset stalk on the cluster three times (not too fast, no too slow, about the rate of singling "Jingle Bells"). You will here a beep. You will now have an extra menu on the MFD that will have a voltmeter.
