Electrically, a battery acts like a constant voltage machine. Current should be able to vary alot while voltage remains nearly the same.

Inside every battery is an effective resistance to the flow of electricity which forms in the series circuit of the battery. As the battery discharges, the resistance increases lowering the voltage developed across the output terminals under heavy load. Now, this resistance is not a real resistor but an effect. When the resistance reaches infinity, the battery is totally dead.

Just recharge it on a trickle charger. That *should* get you going but the original problem likely remains. Most likely a faulty charging circuit.

Edit: I'd see if that battery will hold a charge before replacing it.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

I agree that it is the battery. Find out how they charged the battery (how many amps). If they did a slow charge (2 amps) then I would look for a new battery. If they did a quicker charge then you should try a slower charge before scrapping it. Also, is it a serviceable battery? If it is then you should make sure that the cells are full of water.

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1998 E320 150,000
1980 300SD 240,000
1965 190D 79,000

I do not believe I can add water to this battery.

I am not sure what type of charge it was - it was my friend attaching jumper cables from her car's battery to mine, revving the engine, and waiting. Is there a different way I should've done this?

And YES.... as a matter of fact, it started better than EVER... less than one crank, I swear.

MANY BLESSINGS TO THIS FORUM AND EVERYONE INVOLVED IN POSTING THE THREADS I READ TO COME TO GRIPS WITH THE STUPIDITY OF OTHERS!

Replace that battery... your Benz will love you.

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1983 300TD - 279,000+ (Sat idle for 5+ years... May 1, 2009 - On The Road Again!!!)

You need to use a battery charger. The best way I have found is to use a battery charger set to 2 amps overnight. If you dont have access to a battery charger, then I would use another car with jumper cables. You may have to keep the other car running and hooked up to yours for a significant amount of time before it starts (20 plus minutes). Once you get it started you need to do a voltage and amperage test at the battery terminals. Make sure that the alternator is putting out the correct voltage and amperage. Do some searching here to find what these numbers should be as I don't knoe exactly. If your alternator is working correctly, then you need to concentrate on the battery. If the alternator is proper then you need to properly charge the battery and make sure your connections are good. If the charge doesnt do it then you need a new battery.

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1998 E320 150,000
1980 300SD 240,000
1965 190D 79,000

Yes, with a battery charger....after you have removed the cables and cleaned the cable ends and battery posts....jumping the car from another automobile is only going to give you enough juice to start the car, it is not going to significantly charge the battery...If jumping is the only alternative, then you will want to allow the car to run for at least 1hr after getting it started to actually charge your battery (provided your alternator is working)
You could also try swapping in a new/different battery (take the one out of the jumping vehicle) to see very quickly if the issue is entirely with your battery. Seems like maybe the person you loaned it to could have left the lights on (or door open, or dome light on etc, etc,), light switch all the way to the left is left side parking lights, if I am not mistaken. That alone, with enough time could waste an already weak battery.
Good luck

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On some nights I still believe that a car with the fuel gauge on empty can run about fifty more miles if you have the right music very loud on the radio. - HST

1983 300SD - 305000
1984 Toyota Landcruiser - 190000
1994 GMC Jimmy - 203000

https://media.giphy.com/media/X3nnss8PAj5aU/giphy.gif

Cleaned the terminals, and tried charging it with onna' those portable chargers until it ran dry, but... still, no dice. :/ Took out the battery, gunna' take it to autozone, hoping that's the root of the problem. Wish me luck!

While you're there, buy a cheap trickle charger and an extension cord if you don't have one. You'll be glad you did.

If the battery holds a charge then great. You wont be out the bux for a new battery.

If the alternator isn't working, then you'll have some work to do. Test it with a voltmeter across battery terminals with engine running. It should read between 13V and 15V when it's charging. Manual says 14VDC is average.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

Be aware that sudden battery failure is the normal routine in heavy service applications like your Mercedes Diesel .

Autozone sells : A. crappy batteries and B. usually the wrong one , Wall Mart OTOH has good ones cheaper .

BCI Group 49 IIRC . the wrong ones look similar but only have 850 Cranking Amperes , barely sufficient .

One of my Diesel 123's battery lasted 10 years ~ the other died suddenly on vacation in the middle of nowhere last August ~ don't be ' furious ' just start the car and go shopping for a new one , leaving SWMBO or a friend sitting in the idling car whilst you're in the store ascertaining if they actually have the correct one before you shut it off again .

When the engine is off , reach in and try to turn the alternator by it's fan ~ if it takes a serious shove and the belt squeaks , it's O.K. ~ if you can turn the alternator by it's fan easily or stiffly but silently , the belt is too loose and may be worn out .

Remember : when you start the car cold , DO NOT shut it back off until it's run a while ! .

You cannot charge one car by jumping it with another , that only serves to get you started .

A battery that drops from 12 VDC to 7.5 is either dead or bad .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Alas, there is no walmart around here. Know anything 'bout Sears Auto? My options are Kragen, Sears Auto, Autozone, or Pep Boys...

Sear's Diehard is an excellent battery. Slightly expensive, but why cheap out on this important item? Batteries in gasser cars don't need quite the "oomph" of a diesel application. Buy the right size and you won't regret it.

sears had THE best batteries! imo, I think you are looking for at least a battery w/ 950 cold cranking amps, I just bought one from one of those auto zoo stores and now realize I need to take it back to get one w/ correct cranking amps (950) so it will at least last a while, worth the 20 extra bucks to not have to do the jump thing!!!

Don't you have another car or a friend who can lend you the use of a "Known Good" battery? I would try that route.

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1982 240D 4spd, 327,000mi

The only batteries already here are from gassers, and I'm really afraid of just running THOSE dry, too!

Got a new battery from Sears today, installed it... and she started! Thanks everyone! Gunna' get the alternator looked at when I can.