2000 C280, 103m.

Battery 4 yrs old @ 68m. Voltage regulator replaced 1.5 years ago @ 90m.

Last 2 mornings car would not start. Car starts and runs fine with jump. Battery before no start is 10.8-11.5v. Seems to be charging fine at 14v+ with car running. After driving ~20 miles, battery is at 12.45v.

It is a AutoZone battery and they have checked it twice now and they say battery is good so I must have some parasitic drain overnight.

What are the common places to check?

The only thing odd recently was after pulling into garage, wife says a few wisps of smoke or steam came out of left front hood area. I've checked and nothing seems amiss. Car ran fine after that but a few days later the battery drain started.
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glenmore
1999, 2000 C280
2000 C230K

trunk light or interior light, or light switch is in the left/right parking light position.

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The laws of physics state that "he who sold you the battery will tell you itīs good" and "he who wants to sell you a new battery will tell you that yours is bad."

Obviously your battery is not holding a charge, but is it due to bad plates or a discharge? After shuting down, I would disconnect the ground lead, check the voltage, and in the morning recheck voltage, at which time all will be revealed.

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If there was smoke, something zorched. ( or there is a pending coolant leak. )

12.45 V is pretty low.

When using battery voltage to determine state of charge, the battery must sit for 4 - 8 hours for the surface charge ( temp high voltage ) to dissipate. A round about way would be to run lights for 5 min then let the battery sit for 15 min and retest.

I'd say make sure the battery is fully charged then test from there as driving 20 miles isn't enough to recharge a deep discharged battery.

Lead acid battery state of charge after it has been sitting for a while. This does not test capacity of the battery. As a battery ages the " Gas tank" gets smaller, you can have a full tank but it may have shrunken to a gallon. To check the size of the tank, a load test must be applied, some of the testers at autoparts are more volt meters than load testers.

Voltages are approximate.

12.66 V 100%
12.45 V 75%
12.20 V 50%
11.95 V 25% The battery will suffer some damage if run below this voltage.
11.70 V 0%

+1 on getting a proper load test.

If needed get a OE battery from a MB dealer. About $175 installed including resyncing and disposal of old battery. Call 1-800-FOR MERCedes and they will come to you and do the service with no additional charge.

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Good luck.






1998 E320 Wagon

Things have changed on the roadside assistance, make sure what you are saying is current.

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Yes I know. You must have made a service purchase of $100 or more in the last 18 months to get the free roadside assistance. However, since you are making a purchase (ie the battery) I believe they will come out.

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Good luck.






1998 E320 Wagon

OK, thanks, I knew it had changed. Found out recently, kind of sad.

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Check the door light contacts. I had one on the rear door (exact same car as yours) that was a bit cracked and sometimes it would not shut off the rear interior light, if I closed the door it would push the whole switch slightly into the door jamb, rather than just the plunger part.

And it looked fine until I looked more carefully.

Don't know about your year/model but I was cleaning the dash on my 300E and accidentally flipped the rear reading light switch. Never noticed it until the next day. DEAD!!
Anziani

Went searching for the power drain that I thought was draining the battery overnight. Put the circuit tester on the battery and starting pulling fuses both back in the trunk and up front. Found nothing. My friend suggested unhooking alternator to see if that was causing a drain. Nope. After failing again overnight, took the battery back to AutoZone. They said battery checked out but needed a charge. They did a quick charge and I told them to do another load check, which they did, and the battery passed.

The car starts fine now. We don't drive the car long distances so I got a small 1 AMP charger and put it on the battery overnight. I've come to find that my voltmeter was way off (put it on my friends resting battery and it read 15v+) so once I get that squared away I'll be able to monitor voltages a little better.

So far it looks like the battery drained to a low enough level that just the minor draw overnight would weaken it enough to not allow a start the next morning. It would drive after a jump and start again after stopping no more than a few hours but this was not enough driving to bring the charge back to 100%.

Try a resting current draw test to find the answer, don't chase voltage.

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Just a few mA over spec' will draw off enough to get you a denied start condition.

Anything under 10.5vdc whilst cranking will render all the convenience features into default....like windows express down etc. On some this condition also sets a Low Batt+ code.

In many towed here after battery depletion, many codes need cleared and features reset. Low battery condition causes multiple electronic upsets.

To check for draw you really need a Low Amp Probe that clips around a wire and capable of ranging down to 10mA .

Normal draw should be close to 20mA and drop to this after 90 seconds to 2 minutes as all the modules go to sleep...any draw over 50mA is considered a problem.

My rating of module 'failures to go to sleep' in my experience is as follows :

Seat Controllers left and right.

Rear SAM.

Convenience or Comfort Module.

Front SAM.

Battery Condition Monitor...found under truck latch usually.

Instrument Cluster. ..condensation damage in the multi-plug area.

Alternator ..both low charge rate and/or feed back to ground.

Heat and Air Controller.

Amp for entertainment system.

This list is a compilation of items I have replaced over the years on many different MB chassis.

If you sit in and close the door, the LED cluster mileage readout should go blank in a couple of minutes. If not, something on the CAN is staying awake.

If cluster blanks then check battery load condition for internal leak and level of charge with motor running. You could also leave battery unhooked for 24 hours and monitor battery voltage.

Pulling fuses will not isolate the fault, and most times cause more problems. Don't check for draw like this.

Personal choice ? On any CAN equipped MBZ vehicle is a OE Mercedes battery, especially those with dual battery.


regards

dk



.

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Wow good info here. I had a similar problem a few weeks ago where the 96 e300 wouldn't start after a couple of days of sitting. I hooked up a spare 12v battery to the cables with jumper cables to prevent computer freakouts and took the battery to Advance (where the battery had come from and was under warranty) and was told it was "good but needed a charge." They did a quick charge- I came back and the 750cca battery put out 1000ca. I put it back in, and SO FAR it has been OK. I went ahead and yanked the rear seat out and hooked up my multimeter with aligator clips- and have found things stable now (for 2 weeks anyway). I will check cranking voltage and continue to monitor, I DO know that the measured voltage at my battery when running is 13.4v after the glow plugs are off (11.5 before that) so I have been told to get the alternator output checked, and since many places wil check it for free- it's worth checking out. Thought I'd pass that suggestion along too. Good luck.

Voltage is incorrect, when running should be 13.8 to 14.2 volts.

The term "cranking voltage" makes no sense to me.

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