PeachParts Mercedes-Benz Forum - View Single Post

tenknots · #8 12-17-2004, 08:11 AM

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.