Battery keeps dying... - PeachParts Mercedes-Benz Forum

dgtlmn · #1 10-20-2003, 01:31 AM

I have a 1992 500E. About a month ago I had to get a new battery as it was dead. Would jump just fine, run fine, just wouldn't restart. Now the same thing has happened again. My car was checked out last time, and everything was charging just fine. I'm trying to figure out where I might be losing my juice from. Any ideas??

haasman · #2 10-20-2003, 01:42 AM

The obvious questions:

-Do you have an aftermarket radio and/or radio-amp or alarm system?

-Are the cables well connected to the new battery.

-Is the new battery good? Bad batteries are not uncommon. What brand is it and what rating?

You need to determine:

-Is your charging system charging properly? As simple as a loose belt or possibly the diodes and/or the alternator.

-Do you have an abnormal current draw when the car is shut off that is draining down the battery?

Nice car ... what color? "Sigh ...."

Haasman

y2kimmel · #3 10-20-2003, 10:46 AM

Start your search by connecting an ammeter in line with your negative battery cable (ONLY when the car is off). You should notice a standing current draw. If you're getting any more than 0.1 amps of current with the car off, you can start pulling fuses one by one to isolate the circuit that is causing the power draw.

This is the shortest and easiest way to narrow down your search. The job will be made longer for you, because the fuse box and battery are separated by a lot of space on this car - meaning you'll have to keep running back to the trunk to read the meter after every fuse is pulled.

I had a similar problem on a 1985 BMW 635Csi - it turned out to be a glove box light that wasn't turning off when I closed the lid.

Regrads,
Troy
1995 E420

dgtlmn · #4 10-20-2003, 12:50 PM

for all the advice here! Car has stock radio, everything else is stock too. (oh...it's silver by the way!) Car is supposedly charging just fine according to my mechanic. I'm sure there is something pulling power when the car is off...just need to figure out what the heck it is. What exactly do I need to get to test this? Something I can buy at checker to hook up to my battery?

y2kimmel · #5 10-20-2003, 03:32 PM

A multimeter from Radio Shack should do the job fine. Around $40 - it will be a long term investment for all sorts of projects with your car and house, so it's not a sinngle-use expense.

Shut down car.

Disconnect NEGATIVE battery cable.

Set multimeter to measure current (aka amps).

Connect one end of meter to negative cable lead - one end to negative battery lead.

Check for current draw. I'm guessing that you'll be noticeably over 0.10 amps.

Open your fuse box and start pulling the fuses, one by one - checking any change in the current as measured by the meter. (Replace each fuse if nothing changes with the current). If you find a fuse that, when pulled, causes a noticeable drop in current, then you've found your suspect circuit.

TO THE OTHER BOARD MEMBERS - have i missed anything here? It's been a while since I did this.

Good Luck,
Troy
1995 E420

dgtlmn · #6 10-20-2003, 05:28 PM

without having to get a new battery? you know...since mines dead right now?

y2kimmel · #7 10-20-2003, 10:08 PM

Can you get any power - like to power the radio - out of the battery now? If so - then testing for current draw might work. on the other hand - if it's been a while since the car wouldn't start - it might be completely discharged. You can take the battery out and have any gas station charge it up for you overnight if it's totally discharged.

Regards,
Troy
1995 E420

TX76513 · #8 10-20-2003, 10:23 PM

Y2Kimmell is giving you good advice. Read his first post. Charge battery and isolate the problem through the fuse box. Do you have manual for car to tell you what fuses control what?

Mike Murrell · #9 10-20-2003, 10:46 PM

Consider what Steve Brotherton had to say in this thread:

current drain??

y2kimmel · #10 10-21-2003, 09:30 AM

Make sur ethat the trunk light isn't on - either close the contact switch or take out the trunk bulb. Also - good to connect up the ammeter and let it "sit" for about 5-10 minutes to make sure all of theintermittent power draws that occur at car shutdown have ceased.

Let us know what you find the culprit to be.

Regards,
Troy
1995 E420

dgtlmn · #11 10-21-2003, 01:08 PM

http://www.awsperry.com/awsperry2/awsperry/db_search2.cgi?name=DM-4100A&sort_by=8&submit_search=More&session_key=&exact_match=on&item=dm-4100a

Now I'm just trying to figure out how to use it correctly

Thanks for all the replies and help everyone!!!

tunk · #12 10-21-2003, 02:12 PM

well if the directions that came with it are too technical heres what I know from my own limited use: Bottom left settings are going to be the most useful to you in measuring current draw from battery with power off. you'll disconnect neg term of battery and measure draw from battery by completing the circuit with your multimeter. looks like you'll plug black wire to COM and your red to either mA or 10A and see what your readings look like. Then start pulling fuses one by one and see if anything looks funky. Another piece of advice, go outside and play around with the multimeter. you are probably going to figure it our quicker if you scan the directions once and go try it out, I bet you'll figure it out.

I had a vacuum pump for my central locking system that drained my battery every night. I could hear the thing going with the car off but the multimeter helped me make sure that was the problem (pulling fuse showed less draw on battery with car off than with fuse in place).

good luck,
cdt

MrCjames · #13 10-21-2003, 02:33 PM

Would not hurt to have someone lay in the trunk than close the lid to ensure the trunk lamp is going out when the lid is closed. If it does go out than you will need to remove the bulb while performing the following test.

I noticed your meter is relatively simple in design, cake walk! Disconnect the battery (-), place a test light between the post and the cable, if it stays brightly lit than you have a significant draw. Insert the red lead into the 10A socket on the lower right side of the meter than insert the black lead into the COM socket. With the test light still connected to the battery and cable, clip your Red lead to the Battery Post, clip the Black lead to the cable, remove the test light and read “Current Draw.”

Get back to us with your test value.