On three occasions over the last three weeks, my battery was dead without warning....typical scenario: start car at work (no problems), drive home 40 miles, stop car, pick the kids up, start the car (no problems), go eat pizza, get back in car and find that battery is dead...not enough juice to crank the starter.

On one occasion, I checked the battery voltage after the car would not start, and it was about 9.3 V (dead). I started the car easily with booster pack, drove 40 miles to work, then checked voltage both at idle and with engine off: 13.6 at idle, 12.3 with engine off. Seems ok. I have checked battery & charging voltage several times since most recent dead battery, and the battery appears to take a charge and hold it, and alternator puts out 13.6 at idle.

I just came from Auto Zone where I had them use their machine to check battery and alternator, and both tested OK.

My conclusion is that there must be something drawing a lot of current over a short time when car is off (glow plug relay stuck?, or something similar). However, it seems to be intermittant since I have used the car without any problem for up to a week or so between episodes, then unexpectedly, the battery is dead, after just having used the car. So the culprit appears to be something that works fine most of the time, then unexpectedly kills the battery.

Relevant background info:

1) Battery is 1 year old, nice white MBZ battery. It was drained once in July when starter solenoid was stuck and starter would not go off until I pulled battery cable. Repaired starter, no battery problems since.

2) Alternator is 4 years old, 100,000 miles, Bosch rebuild...seems to be ok

3) The only recent problem with the car which coincides with the dead battery problem was a bad climate control push button unit...just replaced it today. Footwell flaps were not working in economy mode....all vacuum elements tested ok (no leaks) .... I then checked the 5 electric vacuum valves (behind the pushbutton unit)....all worked ok when 12 V applied, but on various push button settings, and heating and cooling settings, the proper vacuum valves were not being activated in certain push button modes. I changed push button unit with a spare, and all is well.

4) Glow plug relay is recent (2 or 3 years old) .... I don't think this is the problem (because its relatively new), but this type of failure would explain the apparent fast battery drain.

5) I dont have any high current accessories in the car...pretty much stock except for a small amp for the radio.

6) Recently, the weather has turned cold...somewhat coincides with dead battery problem, but car operates fine most of the time.


Questions:

Could there be a failure mode in the climate control push button unit that could draw current when the ignition is off??? If this is possible, the unexpected nature of the dead battery could be explained (different push button settings, different ambient temperature, different temp settings, heating vs. cooling modes, etc.)

Could the voltage regulator fail intermitently? (I probably should check electrical connection at the alternator/volt. regulator, and check condition of brushes), but alternator seems to be performing OK.

I'm thinking of wiring up a volt meter from the battery to monitor battery voltage and charging voltage on a continuous basis.

Is there any way to temporarily hook up an ameter to continuously monitor current draw, or do I have to disconnect the positive battery cable to periodically check current draw.

Any other suggestions??


Thanks,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

I have been through the same scenario now three times. Very frustrating.
The first two times the voltages measured about the same as you are seeing, 13.4 to 13.6 at idle, but still my brand new battery would go dead at irregular times.
Turned out it was the battery, had a dead short in both of those batteries. The short was intermittant and did not show up with the electical testing at first. The short did show up soon enough when the battery went 100% dead as I was driving along. The only way to test for an intermittant battery short is to get it out and in the clear, then tilt it away from everything and remove the caps.Run a jump across the two posts. If there is a short the cell that has the short will fizz up like a geyser. Needless to say this is not a safe and sane test, but desperate times...
Next time it was the alternator. Similar problems with intermittant contacts, as they will test just fine, but will fail to work at other times.
You might try removing the battery cables and see if the battery stays charged. Do it on a Friday night when you have some time. If it goes dead with nothing hooked up it is the battery.

Connect a test lamp between the positve battery cable and the post. If the lamp lights with everything off, leave it connected and pull fuses one at a time until the lamp goes out, current draw is on that circuit.

Naturally, it's likely that something unfused can do this too, but you will at least eliminate everything fused.

Once you know which fuse it's on, you will need a wiring diagram to determine the location of everything on that fuse, and test.

Possibilities are radio antenna motor staying on, relays stuck, trunk or glove box lamp on with trunk or glove box door closed, interior lights staying on and you don't notice, and so forth.

I'm tracking down exactly the same problem on my brother's SDL -- got a 0.75A current drain on fuse #15.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I had that exact problem last year........it turned out to be a bad regulator. Some days it was fine others it would overcharge at too high a voltage. Others it decided to drain the battery while car sat.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

My wagon refused to start last Saturday. I hitched it to the charger and it started after about a 5-minute charge. So I took it to a trustworthy battery shop , where they put it on the tester and assured me that there was not a thing wrong with the battery, regulator, alternator or starter.

After ten minutes more I shut it off and came back ten minutes later: it refused to start.

I took off the terminals and roughed them up good inside and out. They were plenty tight before I did this, and there was no obvious corrosion (white or black deposits).

It has not failed again for the past week.

My advice: clean the terminals. A bad contact can keep it from passing enough current to start. The probable cause was a 20-degree F dip in the temperature, I suspect.

I had not cleaned the terminals for about a year. They had a bit of Vaseline and a pair of those "magic" felt circles around each, for what that is worth.

__________________
Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)

Mine drained the battery 4 time over the first summer I owned it, of a couple accaisions it overcharged the rest of the time it appeared fine...and would have tested fine.

Assume nothing.....because the issue isn't consistant. I wasted a new 80 month battery in 14 months as a result.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Intermittent dead battery?

Clean and check your grounds. Battery to chassis and chassis to engine.

I was bit hard by this exact same intermittent head scratcher. (2 starters ) Found the exhaust bracket, where the engine ground strap attached, had worked loose. Tightened the bolts and haven't had nary a problem since. Someone on this forum pointed this out to me.

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Sam

84 300SD 350K+ miles ( Blue Belle )

All good advice so far.

I paid about half of what my car was worth because the PO was fighting a dead battery problem for years and felt the car was unreliable. I found a couple of problems.

Someone had installed a permanent cell phone and wired it directly to the battery. Even with the phone out, I measured a 1 amp draw. Never tracked down the short, just disconnected the wire.

The electric vacuum pump would not shut off until it timed out since there was a vaccum leak in the lock system. I fixed the leak and it shuts off in a couple of seconds now.

Once you've verified that there is no current draw at rest and that the battery is OK, you can be pretty sure the problem is in the charging system.

I think what Whunter posted today would help you:
Amp and volt meter for your diesel?
You'll have to use this type if ammeter since a typical VOM would fry if you tried to start the car with it in series.


Loose cables and grounds can cause you fits. It sounds like a good time to replace all battery cables clean up the ground connection.

As a last resort, you can do what the PO of my car did, install a battery saver that disconnects the battery from the circuit if there is a drain, then reconnects it when you start the car. They run about $80. Here is a place that sells them:
http://www.batterymart.com/priority_start.php
Obviously won't help if the problem is in the charging system.

Your first scenario leads me to believe that it is not a drain. Assuming you take an hour to eat pizza and by then your battery is dead, it would take a huge drain to accomplish that. Only glow plugs could drain a battery that fast. If I remember, the fuse is rated at 80 amps, therefore your glow plugs must draw less than that, and your battery should have 100-115 amp/hours capacity. If your battery was sulfated or had a bad cell or was in any way weak, that would exacerbate the problem. And each time a battery is drawn down completely, it looses a good bit of its life, as much as 50% of remaining life each time.

Good luck and let us know what you find.

__________________
1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer