Dead battery cause? - Benzworld.org

Handy930 · 03-18-2006, 04:53 AM

Lost all power and the engine died. Battery dead. The indicator light did not come on. What causes this to happen? Why didn't the light come on to warn me? 1991 300E 4matic. Thanks for any input on this.

Michael Pillay · 03-18-2006, 06:05 AM

I dont know about the indicator light and how accurate they are. I would suspect your battery or alternator. If I were you, I would pull the battery and take it down to Advanced Auto or Autozone and get it checked. If it is okay pull the alternator and get it checked. Alternately, you can charge your battery, put it in your car. Take a voltage reading. Start the car. Take another voltage reading. The voltage should go up a couple of volts. I am not show how much with your model. If the voltage does go up, the alternator is okay. I would then suspect your battery. Where you having starting problems before this? If you get it clicking sound when you turn the key, it could also be your starter. From your post it looks like you were driving when it lost power so it is not likely to be the starter. But if the battery and the alternator check out okay, I would check the starter next.
I am going to bet it's the alternator. I had a similar experience many years ago. My buick died on as I drove down the expressway. It was the alternator.
Keep in mine, if it is the alternator, find an alternator/starter rebuilding shop. It will save you a good amount of money.
Sorry if I rambled on a bit. Just woke up-working on some coffee.
Mike[:)]

Handy930 · 03-18-2006, 10:56 AM

Thanks for the feedback. I jumped the car this morning and was able to drive it a short distance to a shop. So far the battery checks OK, alternator is putting out 14+ volts and 120 amps and the diodes are OK. Warming it up now to recheck. I'm confused. Hopefully something will show with the heat.

deathrattle · 03-18-2006, 11:36 AM

Have you ruled out something really simple like corrosion on the battery terminals? Or a loose earth strap?

Handy930 · 03-19-2006, 06:15 AM

Will this is the latest. Battery was recharged and checked out OK. Alternator working. Diodes OK. Allowed to warm up for an hour with blowers on, lights on high and no problem. Now I don't know what to do. I did check and clean terminals and check the ground. All seem OK. Plan to leave in two days for a road trip, but now not very comfortable. Any more thoughts?

deathrattle · 03-19-2006, 07:33 AM

^^^
Do you mean you left it idling for an hour with all the accessories switched on? I doubt that the alternator output would be sufficient at those revs to replace the current consumed.

Peter Guenther · 03-19-2006, 08:20 AM

First of all the indicator only shows if the battery is not getting a charge from the alternator, it does not show the state of the battery. The "lost all" would usually indicate a loose battery cable. How old is the battery? If it is 4 years or so replace it. I think a road trip is fine, it should charge it, idling with all the accessories is the opposite. there could be things that stay on, trunk light on my SL, my CD player on the 92 would not eject and kept on running, I had them replace the battery then one day I heard the sound of the motor running. Battery probably needed replacing anyway
If you dont have the Mercedes dealer book get it, they will come out give you a jump, or replace the battery for free (there is a charge for the battery usually low to mid $100s) the same price as over the parts counter. Its one of those lifelong things they offer, they will dispatch the closest roadside person. I think they will even do belts and hoses, I know they dont charge to change a tire. call 1800 FOR MERCEDES

Handy930 · 03-19-2006, 09:08 AM

Will according to the shop the battery maintained during the test and the alternator continued output. I checked this morning and the battery was 12.4 v with the engine off and running the alternator was putting out 14+ volts. If the alternator was good and I just had bad or dirty terminals would the engine die? Do you have to have good battery connections to maintain operation? Thanks for the heads up on the M/B service number. I plan to check voltages for the next few days and on the trip. Hopefully all will be well.

Kajtek1 · 03-19-2006, 10:05 AM

Sounds like bad battery connections. 12.4 V on the battery is on low side, but full test would be under the load. If you can, hook up the voltmeter and see how low the voltage drops during the engine cranking.
I remember, that anything below 10V would call for new battery.
Bad connections can be tricky. I had lot of fun with them on complicated motor-home system. Good-looking eye ends bolted together did carry low current, but kept on failing when I tried to crank generator.
Sometimes the only way is keep the load on and track the cables with the meter.

deathrattle · 03-19-2006, 10:27 AM

On the battery terminals,make sure the contact surfaces are bright.Use steel wool or fine grade abrasive paper.

kajtek is correct about testing the voltage under cranking,but it must be when the battery is at full charge and I suspect it is no longer so.Max alternator output is above 2500 RPM and drops off as the unit ages.