My battery is not holding a charge. I have fully charged my battery 8-10 times in the last few months in order to get it to start. I plug it in at night in insure that the battery and cables stay warm so I have at least one good chance to get the car started in the AM.

Things I know. . .

*Volt Reg was changed out by me in August.
*Battery is 4 years old, tested GOOD this morning at 12.9 whatevers (which is not enough to start the car, he had me turn the car off, then we had to jump it)
*Could not test the alternator, (snowing, cold and nasty)
*After fully charging, I have ONE shot at starting the car. It has to be plugged in for the one try.

New alternator is $100. New battery is $100.

Is it true that after a while the battery is so old and bad that the alternator can no longer charge it? That the battery just won't HOLD the charge?

And how hard is it to replace the alternator compared to say, doing brakes or glow plugs?

I need to have the car running, even if it doesn't have heat.

Thoughts? Advice? I would rather not replace the battery just to find out that the battery is actually still good, it's the alternator.

As usual, you all rock my auto world. . .
Ginny

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Ginny in Denver-ish
78 300SD, 265K (mine)

Alternator is not bad at all.You will see 3 bolts one closest to the block for get it if seized.Uplug your ground all remove other two bolts.Pound alt out.I had my alt. rebuilt 4 months ago,and I'm getting it rebuilt free again.Diodes failed and was draining battery when shut off.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

The best thing i ever did for my car was get an Optima battery. Red top with reverse poles so they match the mb battery. The cranking time you get is phenomenal. You will save a lot of headaches over the life of that battery.

You can take both battery and alternator to auto parts store and have em tested for free.

You can put a voltmeter on your battery with the car running and see what voltage you get. If alternator is working it will be over 13. 14 is a good number.

R&R of alternator is easier than brakes or just as easy. Just don't mess up the tensioner. Loosen all bolts and nuts holding alternator in place and ones on the tensioner bracket so it can pivot before you move the tensioner bolt. The idea is you want the alternator and tensioner bracket to be able to pivot and move freely. I've seen many a bent tensioner bolt (that long thin one with the long hexagonal head that loosens and tightens alternator belt).

good luck.

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

How about a little simple diagnosis before deciding which part to change?

Simply put a voltmeter across the battery and note the voltage. Should be roughly 12VDC. Then start the engine, even if you have to jump it and put your meter across the battery again. If the voltage stays at the same level, the alternator is not charging. If the Voltage goes up to about 13.5 to 14.5 then the alternator IS charging.

Hope this helps.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

get yourself a $5 multimeter.

set it to DC in the 20 volt range

when the car is running, measure the voltage between the two battery terminals.

if the reading is--

lower than 12.6 volts-----then the alternator is shot

higher than 12.6 volts--- (ideally between 13 and 14 volts)---battery is shot i.e. it won't hold a charge

much higher than 14 volts- (say 15 volts)- you are overcharging the battery

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Ben
1987 190d 2.5Turbo

So, this sounds like a dead alternator and not an old battery?

I wish there were still those garages that you could rent a bay in
to do car repair. I don't have a garage that a car will go in (full of crap) so all my wrenching is outdoors. It's snowing today. . .

Thanks

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Ginny in Denver-ish
78 300SD, 265K (mine)

this multimeter is $3



Cen-Tech 7 Function Digital AC/DC Multimeter#

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Ben
1987 190d 2.5Turbo

LOL! We posted basically the same thing at exactly the same time! I would say that "great minds run along the same path" but on this forum that would probably be taken as insulting you.

Anyway it was funny.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

I got it tested this morning at the battery was at 12.9, without the car running. I went to start it back up (off for maybe 2 minutes) and the battery had nothing to give to the car. We had to bring out the little starter machine to get it started again. To start it right now, I would have to charge the battery again. So the battery would show that its charged, but wouldn't actually BE able to start the car more than twice before needing a charge.
What does that mean?

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Ginny in Denver-ish
78 300SD, 265K (mine)

I understand that! Last Winter, the starter in my pick up gave up while it was in the driveway with six inches of snow on and around it. It was the starter, so I couldn't get it in the shop on the lift.

I had to crawl around underneath in the snow and it was quite a challenge.

Best of luck with it. At least you won't have to get underneath.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

get the car running somehow and do the test while it is running. If you find the voltage to be between 12.6 v and 14 v then you need a new battery

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Ben
1987 190d 2.5Turbo

A resting battery showing a voltage of 12.6 does not really help with the diagnosis.

How it handles a 'load' and then comes back is the test.

If you live in Denver with a diesel car with a 4 year old battery, you need a new battery anyway.

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Ben
1987 190d 2.5Turbo

Sounds like battery problem to me. It is not holding the charge. Any good battery can crank the engine a number of times when fully charged.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Many AutoZoos will test your system for free, good luck.

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83 SD

84 CD

You can often troubleshoot using nothing more than the headlights.

Think of the headlights as your volt meter. Turn on the lights either with someone to observe them or with them shining on a surface such that it reflects well enough to see any change in brightness.

With the lights on and trying to run the starter, they will normally dim a little bit while the starter motor is turning, but once the engine starts they should be a little brighter than when the engine was not running.

Also if the headlights shine seemingly okay, but when hitting the starter, they go to nothing or near nothing, the battery is weak or dead.

Hope this helps.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution