diagnosing a dead-battery

[ke6dcj]

My wife called and said the W124 1993 500E wouldn't start. She diagnosed it as a dead battery, and I agree.

After installing a fairly new OPTIMA fully-charged, and the engine running the voltage read on 13.8VDC on my Fluke meter.

The same alternator (150-amp, 14 VDC, 1999 S500) in my wagon reads 14.1VDC, AND when I installed on the 500E over a year ago, I also tested 14.1 VDC.

The "battery" light on the instrument cluster isn't lite when driving, AND the voltage regulator is barely 14-months old.

I'm guessing either a bad alternator or regulator.

Any ideas ?

BTW: the "snow chains" button doesn't work anymore . . .

All fuses have been checked everywhere and tested good continuity (all less than 2-years old).

Neil

[samiam4]

Voltage is a good data point- but you need amperage man!

You need to see how many amps the alternator is putting out. The battery should be correctly charged and properly load tested.

'

Michael

[Ron Johnstone]

13.8 is probably within specifications and should keep the battery charged. I'd check for a battery drain such as a light that stays on when it shouldn't. Check the car at night in total darkness. I found a door light on my SD that was slightly glowing that would discharge my battery over a week. The quick way is to check amperage flow from the battery when everything is off. There will always be some flow to the clock, etc. but not much. If you don't have a amp meter, pull the lead and check for the magnitude of the spark when you touch it to the battery - little spark = normal, fat spark = a problem. Of course, you could simply have had a bad battery. They do short out occasionally.