Battery or charging problem? - PeachParts Mercedes-Benz Forum

Wasuchi · #1 08-04-2004, 04:39 PM

For the last month or so I've had problems if I leave my lights on for few minutes (maybe 5 minutes) or leave the radio playing while the engine is off etc. The battery is dead almost immediately which led me to believe it was going bad.... I took it off and had the parts store test it and it showed to be good and took a charge just fine. So I checked it's voltage sitting in the car (at this point thinking that the alternator isn't putting out enough), 12.55 with car off, the voltage at idle is 13.65 and at 2500 rpm is 13.7. Is it getting charged enough, bad battery, or is there something else wrong? (I'm out of ideas at this point!)

R Leo · #2 08-04-2004, 04:51 PM

Sounds just like a bad battery to me.

#3 08-04-2004, 05:42 PM

I am in the midst of sorting that out here. Had the battery going dead every few days , etc..
I kept checking the voltage and it was showing low 13 vlts + when idling. Thought that was low, but still it was charging some.
Finally I checked it and the voltage was down to 11.9 v when running. That time frame was 3 months. I would guess the alt brushes were wearing down.
I replaced it with a used I had in hand, voltage now at 14.1. Much better, but I will still rebuild the original and put it back in there. This one squeels sometimes and is not charging that well. Still have a slow start some mornings.
I have been told that these really need to put out over 14 v for a robust charge. Best way to check them is with lights, blower, and rear defrost running. Should still show 14.2 - 14.3 volts. Anything less may show that the it is not charging sufficiently.

Wasuchi · #4 08-04-2004, 08:58 PM

Tested again with lights, ac, and radio on and voltage dropped to 12.22 at idle and 13.25 at anything over about 1000 rpm's. So....... I guess I'll see what happens with new brushes and voltage regulator, hope that fixes my problem.

Mr. FancyPants · #5 08-05-2004, 10:07 AM

You need to measure a batteries worth with a load type battery tester. Even a bad battery can show sufficiant voltage, but cannot produce sufficiant amperage.

If your alternator is putting out 13.7 this indicates it is working properly. Your average auto battery (starting type) last only about 5 years.

The DieHard International batteries that most of us here use may last a bit longer.

Wasuchi · #6 08-05-2004, 10:45 AM

The parts store did measure with a load tester and it showed to be good...... the tester estimated CCA at 610 when it says 750 on the battery, so that makes me think the battery isn't that good. It's an Interstate 60 month battery going on 46 months so I'll be carrying a set of jumper cables with me until I'm sure it's the battery that's the problem.... then I'll replace it.

Mr. FancyPants · #7 08-05-2004, 10:53 AM

Sounds odd that with a good battery, and a working alternator, that your battery should go dead so fast, or at all!

Maybe you need to check grounding straps as this would be likely your next look!

Jim Anderson · #8 08-05-2004, 10:59 AM

I had a weak big diesel battery I brought into a battery store once. They hooked up a battery tester that had a heater on it. It glowed bright red for a second and the guy pronounced the battery good. I said "Do it again." He hooked it up again and it again glowed red, then after a second went out. The guy then said "I guess you do have a bad battery." A bad high capacity diesel battery will show good when tested as a low capacity gas battery, but I knew better.

If you're getting a good voltage under load when the car is running, its the battery.

How old is the battery?