[sl450]

Fo some reason, if the car is not started everyday the battery dies. This is the 3rd battery in four month.

Is their a switch or relay that is known t cause this?

Thamks!

 

[spanners]

Draining battery

This could be caused by anything from the boot(trunk) light staying on to a faulty alternator.

If you have a 12v test light, it is a simple process of elimination.

Disconnect the battery earth when the battery is charged and then connect the test light between the negative terminal and the disconnected lead(the positive side of the battery must remain connected). If there is nothing draining the battery, the test light will not be lit. If it is lit, the brighter the light the bigger the drain.

If there is a drain, remove and replace each fuse in the fuse box one at a time until the light goes out.
Then see what works off that fuse and you've found the problem.

If the light is still on after you've tried all the fuses, then it is either a non original peice of electrical equipment causing the drain or the alternator or starter motor.

 

[ckb]

If your battery is being killed it will be the alternator. I had the same problem. The alt...

If your battery is being killed it will be the alternator. I had the same problem. The alternator is over-charging due to a fault in the voltage regulator. This fries the battery until it wont hold enough of a charge. Of course, the charge light remains out leading you to think all is well!
Change the alternator and all will be well. I got mine for £54 in the U.K..

 

[Don36]

Battery Drain Problem

I had the same problem on my 1982 380SL. I still have trouble believing what was happening but I give it to you as an example of what can happen.

I pulled the hot cable from the battery and put an amp meter between the post and the cable. It showed there was a significant amp flow. Then I pulled the fuses one at a time and looked at the flow. When I pulled #1 fuse the flow went away. Checked to see what that fuse feeds. I started with the trunk light even though I had verified it was being extinguished when the trunk was closed. When I removed the bulb the amp flow went away. I replaced the bulb but the flow returned. My conclusion is that the trunk light switch shorts when a bulb is installed. Can't explain that but don't know what else could be happening. So have left the bulb out until I can find and replace the switch.

Bottom line - don't go out and start buying new parts until you or a good auto electrician who understands MB's has pinpointed your problem. It could be just about anything!!

Am a newby (first MB) and just a shade-tree mechanic but had never encountered this before. Anyone else??

Don36

 

[spanners]

Battery drain

Don, could yours be a bad earth in the boot (trunk) somehwere?
The bad earth could be causing some other electrical circuit to earth through you bulb.

 

[Don36]

Battery Drain

Haven't done anything to it since I removed the bulb. But that's a good through and I appreciate your mentioning it. Hadn't thought of that. I'll check it out as soon as I get it back from the garage. Right now it's in for rebalancing the drive shaft, replacement of shaft bushings, bearings and mount, and replacement of the right rear axle assembly and outer bearing. Trying to resolve a rumble/vibration and high speed whine. This beast is going to send me to the poor house!!

Don