What could be draining my battery? - PeachParts Mercedes-Benz Forum

dieseldaddy · #1 05-13-2002, 03:01 PM

OK, I have been searching this topic for a while and always come to some stumbling block.

I have a 1981 300tdt and I purchased an Optima "red top" battery with 950ca and 850cca to replace the 550ca battery from Texas life. ("Hot" in Michigan is "Cold" in Texas!)

Problem is, I have had to FULLY recharge it 6 times since the beginning of February (when I purchased it).

The voltmeter reads 12.0-12.5 when sitting fully charged, and 13.8+/- when idling.
That tells me that the alternator is doing it's job...right?

Here is the history: My wife's car, driven most days, short 4-7 mile trips. At least once a week we drive it for extended periods on longer trips, but still nothing major. I have recently been taking it to work (26 miles each way) once a week, and we DO drive it all weekend.

THE ONLY THING I can think of is that when I installed a new CD player, I have to rig up a wire for the channel memory directly to the battery... could this be the culprit?? hard to believe...

Just learned that the PO had some trouble like this, but it was more hard cranking issues...with a 550ca battery i can imagine! THAT problem seemed to remedy itself with the purchase of my new battery.

Questions#1: Could this be the Voltage Regulator even if the alternator is giving us these good readings? How do I test it.

Question #2: How can I test to see if there is something (like a stuck glow plug?) drawing current while the car is off?

**Please dumb-down your responces a notch or two as I am electronically challenged. Thanks~

ANY suggestions gladly accepted!

oasis100 · #2 05-13-2002, 05:08 PM

Hey, I had the same problem a few weeks ago. I took it to the mechanic and after 2 weeks the guy found out what was wrong with it, apparently the cheap ass becker radio was not turning off properly or something and was draining the power over night.

Since you just installed a new cd player, I would definitely say it's that if your problem started after installing the CD player.

My car is working fine now after disabling the beker radio. i've got to get rid of this junk.

Jim Anderson · #3 05-13-2002, 05:42 PM

4-7 miles will kill a diesel's battery, it isn't enought time to recover from starting. Maybe consider another minuit of warm up time. And 13.8 volts seems a touch low, almost 14.5 volts is more normal. I think newer cars seem to have the regulator set a little higher than they used to be. Just for grins cause it's not too expensive you could replace your regulator. Being electrically endowed I think I noticed regulators being temperature sensitive, on purpose, the voltage is a little higher when cold and drops as it warms up.

blackmercedes · #4 05-13-2002, 05:49 PM

My 190E had a battery drain problem. After shelling out $1000 to the dealer to replace parts, I gave up and took it to another dealer. They found a sticking relay, and the problem was solved.

thebern · #5 05-13-2002, 09:47 PM

I suspect the radio/cd player wireing connections!
In my ford truck the battery would drain dead every two weeks if I did not drive it. I started removing the faceplate of the pioneer cd/radio player and the vehicle will start right up after sitting for 5 or 6 weeks. Seems that the radio was draining the battery.
I only use the truck to go to the dump or hardware/lawn and garden store. Good luck.

#6 05-14-2002, 06:50 AM

This should be relatively simple to troubleshoot.

Disconnect the negative battery cable and place an ammeter in series with the cable and the battery. If you see a drain with the key and all accessories turned off (don't forget to close the doors and trunk) which you probably will, then start removing all the fuses while watching the ammeter. When you pull a fuse that makes the ammeter go to zero, you've found the circuit. Even before pulling a fuse, I would remove the radio wire you were talking about and see if that is the culprit. If it is, the ammeter will go to zero.

Somewhere there is something on, or shorted causing the drain. By monitoring the drain while you disconnect things, you will find the offending circuit.

Good luck,

Jim Anderson · #7 05-14-2002, 11:28 AM

Wait a moment after you close the door till the inside light times out.

dieseldaddy · #8 05-14-2002, 03:19 PM

Jim,
My light goes out instantly when the door is closed...
Is this the correct behavior?

I noticed that in my '83 240D the light DOES stay on for a while, but in this '81 300TD it goies out right away.

dieseldaddy · #9 05-14-2002, 03:22 PM

Alright, thank you EVERYBODY for your responses!
Again I am amazed at the knowledge and willingness to help a brother in need.

Well, I am 99.92% sure I found my problem. Back a while, I had a silmilar problem, and I did not remember it until last night when I got my FREE replacement battery (new 7-year warranty to boot!) and installed it only to have it not even 'click' when engaged.

The REST of the story goes like this:
One of the PO's had apparently had either an alarm system or a CB or something under the dash and the wiring was (is) a total disaster!!
I noticed it when I was fixing the interior dome light a while back and had to remove the below-the-dash panel to get at the ground.
Well, I noticed that there is ONE white wire down there that apparently attaches to the ignition switch that when attempting to wire for alarm/cb/whatever, they just cut the wire covering and wrapped another wire (no connection, tape, or anything) around the original wire. This had vibrated loose, but not off, which would be giving the appearance of spotty behavior.
Tried to start the car and nothing, tightened the wired connection and VROOOM! (actually," va...va...va....rrr.rrr.rrrrrrrrrrr.oooom") we were fixed...for the time being.

Somehow, I had pushed that memory to the basement of my brain because I did not remember this until I had replaced the battery and it sould not start. I got back under the dash and sure 'nuff, the wire was now totally off. Tried to start the car, nothing, wrapped the wire back on and she started right up!

Tonight I am going to make a *real* connection and soon I will attempt to return the whole wiring mess back to as *original* as I can.

Whew, sorry for the long description, but it sure is good to know what was causing what I thought was a "drain" was actually just a loose/disconnected wire!!

Thanks again everyone!
~Brian