I have a 91 300sl and Ive replaces the battery wih a new interstste. But after about 2 days parked the car is dead. I noticed that if i gently rub the neg post of the battery with the negative cable, I get some small sparking. Ive read all the past posts and Ive removed every fuse I could find and still the same. Also I dissconected the radio and Alternator and still does the same. What the hell is going on? ANy Ideas anyone????? THanks guys.

First, was there anything wrong with the battery you replaced or have it bench tested? Second, is the charging circuit operating properly (alternator, voltage regulator)?

The sparking is normal, this means there is at least some voltage in the battery. When you go to start the car, do you at least get a click of the starter soleniod, or is she completely dead? Do you have a basic volt meter? If you do check the voltage of the battery with the car running, presuming you get it jump started. With the engine running, you should be getting 14V on the battery terminals. If you are not getting this, you alternator is shot. With gasoline cars, everything is powered by the battery which is constantly being charged by the alternator. Once the alt. falls behind the electrical demand of your sparkplugs, power features etc. the battery has to burden that load on it's own. With all the electronics your car has, it wouldn't take long to kill a battery. If you don't have a basic volt meter, you can buy one at any autoparts store for $5-$10.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Return the battery and have them do a voltage test and check your alternator. I'll bet you you got a bad battery. It happens. Otherwise you have some minor draw that's draining it.

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1999 C280 Sport, 1967 911s Porsche

The Battery was tested and its fine. The car will hold juice for about 2 days then its just dead. When Im using the car daily, It wont die, Ive tested the alternator and its ok. What setting do I use on the muti meter and what reading is normal for draw? What else can be drawing from the battery when its not in use. ABout the previous battery, The car was in the garage for a while and the battery that was in it never would hold a charge. Basically it was junk so I replaced it with a new Interstate. tHANKS Guys.

You need to use the miliamp stting on your meter. The normal draw on your car should be around 40 to 50 miliamps after all the control units have shut down. On this car you can have a 500 miliamp draw for up to about an hour after turning the car off, so you need to allow for that to see what the actual draw is. Several things that are prone to cause problems are the antenna and the cd player. Also be sure to have the trunk light turned off during this test.

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Mercedes Benz Master Tech - Retired

Ya know thats funny you mention the antenna. A few weeks ago I got into the car and it rained and my power antenna got wet. I didnt have the rubber seal on it and it I guess blew it. I took it apart and found a burnt piece inside. Also the battery was dead. I dissconected it and replaced the fuse but it still draws over a few days. Does that change anything??? Thanks alot.

You need to do the draw test to find out what circuit is at fault. With the amp meter connected in series on the negative battery cable check the draw. You need toconnect your meter to the negative battery and to the negative terminal on the battery before fully removing the cable from the battery. After doing this wait for about an hour for all the computers in the car to power down. If after an hour wait you have more than a 50 miliamp draw you need to start reomving fuses from the fuse boxes one at a time while watching the meter. When the draw goes down you have found the circuit you need to check.

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Mercedes Benz Master Tech - Retired

Turned out to be the cd player. I used a multimeter in-line with the negative battery cable. As soon as I would complete the connection, I would read about 3.5 for the first 10 seconds or so. Then it would drop down to the normal range of .012 or so. When my cd player was plugged in, the reading would never drop past 2.6, so I knew this is where the problem was. Turned out to be a cd jammed in the changer that wouldn't let the unit turn off.

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Jon
'92 500E

ok, I tested the battery with the meter by connecting it in series with the neg cable. I removed the cable and connected one of the meter's prongs to it and the other meters prong to the neg battery post. Now the meter has 3 amp settings; 100ma, 10ma, 1amp. on all of the settings the needle pins. I switched the setting to voltage and it shows 14+ volts. I tried it with the cable still connected to the batt post and it shows nothing. I noticed that the fuses in the truck are always hot and few under the hood remain hot all the time. Also I tried probing the battery normally by going from neg to poss with meter and it reads 14+ volts and it pins the needle when I switch to amps. What am I doing wrong??? Thanks Guys!

since your meter only goes up to 1 amp, and i'm sure you're pulling more than that 'cause of your drainage issue, your meter probably won't be able to register the reading. i actually blew a fuse in the first meter i used since it wouldn't read high enough. i'm not quite sure what the optimum reading is, but i remember seeing like a .012 - .016 amp reading at normal running range. before i fixed it, i was getting reading almost up to 3.0 amps. so when you isolate the problem by removing fuses, you should see the reading go way down and readable when you pull out the problem fuse. hope this helps.

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Jon
'92 500E

Start with the 1 amp setting, and work your way down.
The voltage is not important here.

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1986 300E 5-Speed 240k mi.

Hey Jon, what was the problem anyway?? I have to get a better meter, tomorrow. But am I checking it correcetly?? Do I run the meter inbetween the neg cable and neg post? Thanks guys

Yes, you are doing it right - to measure current you need the meter in series in the circuit, hence the meter is between the neg cable and neg post.

Cheers.

my cd changer. it had never worked since i bought the car last december. i didn't notice this problem until recently when i got a 2nd car and was not driving the 500e daily. there was actually a cd jammed in the player that was somehow making the changer try to do something, hence the issue. as soon as i took the cd out, problem was gone...and my changer works just fine.

i've heard about drainage issues related to cd changers and also power antennas. if you have a changer, try unplugging the power to it...or just pull out the fuse in the back...and see if the reading drops.

my first multimeter was a $20 job from home depot. i really didn't know what the heck i was doing and got one that wouldn't read high enough. a friend of mine brought his over, much better one, and we had no problems getting a reading in-line with the neg cable and post.

let us know how it turns out.

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Jon
'92 500E