Battery Problem...?? - Mercedes-Benz Forum
 
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#1 (permalink) Old 05-30-2012, 02:45 PM
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Battery Problem...??

To start I have a '08 C300 the only modifications is a aftermarket sub which I have confirmed shuts off when I turn the car off.

So this story starts a few weeks ago..

1. I was trying to turn my car on it would start to turn over for the standard time but then would "Time out" what seems like just before the car starts. Tried this for a while with the same results. I then had my car jumped and it worked.

2. (This all happened on a Sunday so the only place open was Pep Boys) Took my car into Pep Boys, who tested my "Electrical System" and came to the conclusion that it was just a bad battery and replaced it..

Worked fine for a few weeks

3. Today go to start my car and same issues as the start... Sort of turns over but not long enough to get started. I had to leave for work so I couldn't try to jump it but I assume it will start again if I do. I called Pep Boys to confirm they actually tested my electrical system (Mainly sounded like an alternator issue to me) and long story short don't think they tested it.....

So has anyone else had this issue?

Does this sound like an alternator issue?

Any thing else to try?



Thanks in advance,
-RJ
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#2 (permalink) Old 05-30-2012, 03:07 PM
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It's possible it's a bad/defective battery.

I've seen that happen with a new battery from Walmart (on a family member's Subaru), a few weeks after purchase.

S.


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#3 (permalink) Old 05-30-2012, 03:36 PM
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Your car seems to run fine aside from not being able to maintain enough battery power. You can test if the alternator by running your car and unhooking the battery. If it continues to run, it's the battery, but if it dies then it's the alternator.

If it is a defective battery, you should be covered with the warranty of the battery. Look for a battery with the longest warranty to avoid being scammed. I purchased a battery a month ago for a different car that came with a 7 year warranty.
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#4 (permalink) Old 05-30-2012, 06:42 PM
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Your car seems to run fine aside from not being able to maintain enough battery power. You can test if the alternator by running your car and unhooking the battery...
I am not sure but heard from my friend that never disconnect battery when alternator is running. Reason is battery not only provides electrical power but also acts as a tank (spike absorber); without it, alternator generates random spikes which could damage the electronics system. Maybe the new car design has considered that. I have used a plug-in volt meter to monitor 12V outlet. When my car is running, voltage goes from 12V to like 13.4V. that indicates alternator is working, charging the battery.

Last edited by C300HE; 05-30-2012 at 06:45 PM. Reason: more info
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#5 (permalink) Old 05-30-2012, 09:00 PM
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Originally Posted by C300HE View Post
I am not sure but heard from my friend that never disconnect battery when alternator is running. Reason is battery not only provides electrical power but also acts as a tank (spike absorber); without it, alternator generates random spikes which could damage the electronics system. Maybe the new car design has considered that. I have used a plug-in volt meter to monitor 12V outlet. When my car is running, voltage goes from 12V to like 13.4V. that indicates alternator is working, charging the battery.
*Unhooking the positive terminal Or if he has the proper tools such as the multimeter, then that would be the easiest route.
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#6 (permalink) Old 05-31-2012, 08:10 AM
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I am going to take it to another mechanic tomorrow that I have had good luck with in the past fixing problems. I have heard a few things though:

1. How many batteries does the C Class have? (I probably only had one replaced)
2. Have you heard of the computer for the power seats staying on and draining the power?
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#7 (permalink) Old 05-31-2012, 09:05 AM
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2. Know nothing about the power seat standby current, but know that C has got a smart battery management system. I noticed a few times that after I parked it in the garage, the fan nearby the battery turned on for quite long thime maybe 30 minutes or so. Opening any door or trunk lid will stop that fan but once door or trunk lid is closed fan starts again. Opening the hood will not stop the fan.

I measured my other cars when everything is turned off. Standby current is 70 mA on RX300, about 100 mA on RX300. Forgot what battery I have from Costco, but it will take about 3 weeks of no operation (no charge) to fail the startup.

C battery terminal is not easily accessable so I don't want to mess it up with my current measurement.

Last edited by C300HE; 05-31-2012 at 09:07 AM. Reason: more info
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#8 (permalink) Old 06-01-2012, 07:49 AM
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OK the plot thickens... Took my car into Vaia Auto (Vaia Inc Auto Specialist - Fulton Market - Chicago, IL) here in Chicago, who has helped me in the past and knock on wood always honest.

They have said that it is not a battery problem for sure, because the car is starting but then turning off.



AGHHH more problems
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#9 (permalink) Old 06-06-2012, 11:58 AM
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Just wanted to give everyone the update.. The guys at Vaia have been looking at my car for a few days now and replaced a fuel sensor they found that was going bad, but also think that the issue may have been with the key I had. I was at work at and they went out of their way to send a guy over to my house and get my back up key from my neighbor tested it and it works fine. So not sure if it was a fuel sensor issue not putting out the correct PSI for the fuel or the the key but my car works!!!! (They also cleaned out my old key and put in new batteries so it seems to be working to) now knock on wood is just keep working.

-RJ
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