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  #1  
Old 05-08-2003, 02:20 PM
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Battery Dead??

I replaced the battery 4 years ago on my 1989 300SE with a new OEM one. I drive the car on weekends, and usually for long distances, and have not had a problem starting the car until this past weekend. The first start on Saturday was weak and it got progressively worse to the point of being a non-starter by Sunday morning (thankfully in the garage). Can a battery give-in in 4 years? When the car was running power appeared good...lights ok, radio, etc. Can the alternator be causing a gradual drain of the battery? How can I test the battery? Any advice greatly appreciated.

Thanks.
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Last edited by geoellis; 05-08-2003 at 04:17 PM.
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Old 05-08-2003, 04:09 PM
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The OEM batteries are generally pretty good...save for unusually harsh conditions, you can get 6+ years of life.

Easiest test would be a voltmeter across the battery terminals. Nominal voltage should be 12V of course, but if your battery is dead, you will see less than this.

If you can get your car started, again, measure the voltage, ensuring that accessories are off (radio, wipers, headlights, etc.). Your alternator should be producing 13.5 - 14.4V.

Anything outside of that range, and the culprit is the alternator. But more than likely, the voltage regulator needs to be replaced...the brushes have worn out.

I believe on your model, the regulator (about $30) can be replaced without having to remove or replace the alternator. Later ones have an internal regulator that requires swapping out the alternator.
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Old 05-08-2003, 04:21 PM
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Thanks G-Benz, I'll give the voltmeter a try. By the way, I would guess that if the voltage regulator is external it attaches to the exterior of the alternator?

George
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Old 05-08-2003, 04:23 PM
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4 years is not great, but not unheard of either. There are many factors that effect the lifespan, including heat, vibration, initial shelf age, number of deep discharges, freeze ups...

Check the terminals first. Clean and lube as needed.

Check the water level in the cells. May be low after 4 years. Add distilled water as needed, and recharge fully, ideally with a battery charger.

Note: for a discharged battery, do not fill completely to the line, since the level will rise as it charges, and it may overflow.

For testing, a voltmeter is the way to go.

Car off, charged battery should produce at least 12.5 volts, preferably more.

At 2000rpm, no accessories on, you should get around 13.5volts.

At 2000rpm, with high beams on, rear defog on, blower fan on high, you should get a minimum of 12.5volts.

Best of luck.
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Old 05-08-2003, 04:28 PM
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Quote:
Originally posted by geoellis
Thanks G-Benz, I'll give the voltmeter a try. By the way, I would guess that if the voltage regulator is external it attaches to the exterior of the alternator?

George
The regulator is held in place by two screws on the back of the alternator housing. The regulator just pulls right out.

Mine is different so I can't tell you how accessible it is, or whether or not it can be done without removing the alternator.
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  #6  
Old 05-13-2003, 11:01 AM
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All, thanks for the advice. Here's an update: I had both the battery and alternator tested and it did in fact turn out to be a dead battery. It's intertesting how they can just fail instantly with little warning. Anyhow, I opted for the OEM battery for $100 and all is good to go.

Cheers.
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  #7  
Old 05-13-2003, 11:15 AM
I told you so!
 
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This is what I know and my experience with automotive batteries:

- Batteries have a finite number of deep discharge cycles.

- Batteries often last only 4-5 years. They can last longer.

- Try to install the largest size battery that will fit in the space on the battery tray. Sometimes new car manufacturers install small batteries to save on weight. The larger sizes last much longer.

- The Mercedes manual recommends trickle charging the battery every three months for a car in storage.
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Last edited by Kestas; 05-13-2003 at 02:15 PM.
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Old 05-13-2003, 12:23 PM
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If the car has sat idle during the work week for 4 yrs and you got 4 yrs. out of the battery, you did quite well. I used to get long life out of car and motorcycle batteries, but in the last 10 yrs. or so, it seems that 3-4 yrs. is about as good as your going to get unless you buy one of the highly touted Optima's.

One thing's for sure. Your charging system is doing it's job and you have little or no battery drain.
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  #9  
Old 05-13-2003, 01:38 PM
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You are right about the infrequent use. Better for the battery to be "topped-off" daily by the charging system than to sit and slowly drain during the week only to be "recharged" come the weekend. I guess this is where a trickle charger will do the trick and potentially extend the life of the battery.

Nevertheless, I was flipping through my service records and realized that I was sorely mistaken as to the age of the dead battery. I purchased it in October '97 so I guess 5 1/2 years is more than respectable, especially given the conditions of use. Boy how time flies. Bodes well for those OEM batteries.
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