Sudden (I think) Battery Problem - PeachParts Mercedes-Benz Forum

RML · #1 01-16-2009, 03:12 PM

So things were going along nicely, my car was starting OK, then it got a lot colder. The 84 was starting to crank a little slower and I thought it was just the cold weather. I plugged in the block heater overnight and thought all would be good to go in the morning, but the battery wouldn't turn it over. I tried to jump it with my van but it still wouldn't turn over. So I got suspicious. I pushed it into the garage and put the 85 battery in the 84 and it turned over and started perfectly. Not much cranking at all.

I looked in the 84 battery and the water was low. I filled it with distilled water and put it on a battery charger.

This morning I expected to jump in and start it up, but when I turned the key, nothing. No cranking with the 85 battery that was strong the night before. So I assume I have a short somewhere. I am not the best with electrical problems, so where should I start? I picked up a battery tester on my way home today to test each cell of the 84 battery that is charging. The tester is the kind that you suck up some acid into and it gives a reading based on where the guage is floating. Specific gravity, I think it is based on, I guess on the concentration of the acid.

If I can get it started with a charged battery I may pick up a battery terminal cutoff switch so I can prevent it from draining. A friend recommended a good alternator shop that may be able to do some diagnostics for me.

Any other suggestions will be much appreciated.

Jeremy5848 · #2 01-16-2009, 04:00 PM

The standard test:

First, make sure the car is off – use the "key in pocket" safety procedure. Close all doors. Nothing should be "ON" in the car.
Next, disconnect the negative cable from the (charged) battery.
Then put a VOM set to "DC Current" in line with the negative cable. There should be a very tiny amount of current due to radio memory, clock, etc., but only about 10-20 milliamps (1 milliamp = 0.001 Amp).
If you have more current, something is "ON" that shouldn't be.
Try pulling fuses one at a time until the extra load goes away. Your problem is on that circuit.
Until you find and fix the problem, you can disconnect the negative cable overnight. That will keep the battery from discharging.
Keep a trickle charger on the battery overnight. It will keep the battery topped off and will also keep it a bit warmer due to waste heat from the charging process. Both will help the batter work next morning.
Let us know what happens.

Jeremy

RML · #3 01-16-2009, 04:05 PM

Thanks Jeremy. This sounds like an excellent place to start. I'll report back.

rrgrassi · #4 01-16-2009, 04:22 PM

Battery problems in the hot weather or cold weather, can spring up suddenly.

RAYMOND485 · #5 01-16-2009, 04:23 PM

1984 300D TURBO 148K
REPLACE THE BATTERY $100.00 plus core $12.00 7 YEAR 2 YEAR FREE REPLACEMENT, 950 CCA, GET A 8 YEAR 3 YEAR FREE REPLACEMENT. MAYbe $140.00, take NEG CABLE OFF AND INSTALL NEG CABLE LAST, CLEAN BATTERY CABLE WITH A WIRE BRUSH, CHECK ALTERNATOR OUTPUT 13.2 - 14.2 USE A CIG LIGHTER SOCKIT NEXT TO ASK TRAY PLUG IN DIG METER BUY AT ANY AUTO STORE SAME PLACE YOU BUY YOUR BATTERY AND BATTERY POST AND CABLE CLEANER MAYBE $5.00

Brian Carlton · #6 01-16-2009, 08:56 PM

Quote:

Originally Posted by RML

Thanks Jeremy. This sounds like an excellent place to start. I'll report back.

Why have you concluded that you have a current leak? That's usually the last suspect. When the temperatures drop, any battery that's more than four years old is immediately suspect when it comes to starting a diesel.

Pull the battery, bring it indoors, and charge it overnight. Then, take it to one of the McParts (Autozone for sure) and have them load test it. They'll tell you in two minutes if the battery has the required cold cranking amperage required for the diesel.

If it's me...........and it's more than four years old...........I don't even bother with the test..........I buy a new battery at Autozone and install it. DONE.

RML · #7 01-16-2009, 10:01 PM

Quote:

Originally Posted by Brian Carlton

Why have you concluded that you have a current leak? That's usually the last suspect.

I concluded it was a current leak because I put the battery from the 85 in and it was really strong. 8 hours later, after being connected to the 84, it was dead. I even had the block heater on all night so the engine was warm and it wasn't cranking an ice cold engine. This was also inside my garage, above freezing.

The battery may be suspect but I still think there is something else going on. Tomorrow morning I'll get a meter and run through the suggested diagnostic steps. I will probably end up with a new battery but I want to make sure there is not another problem going on.

RML · #8 01-18-2009, 01:25 AM

Thanks, Jeremy, for your clear instructions.

I got a battery tester and found that the battery that was originally in the 84 looks shot. It doesn’t seem to want to take a charge and there are differences in the values I am getting from the cells of more than 50 points on the tester scale. The instructions on the tester say all cells should read within 50 points. All cells are reading in the “discharged” area after having the battery on a charger overnight.

I removed the negative cable and put a meter between the negative terminal and the negative cable with everything off and found that something was drawing about 3.5 to 4 amps. I sequentially removed fuses and found that number 2 was the culprit. The antenna turned out to be the problem. I have had some problems lately with the antenna not going all the way down when I turn the car off, so this pointed to the antenna as well. I unplugged the antenna in the trunk and the current drain stopped. Now when I test the current, it starts out drawing .25 amps, quickly drops to .03 and then drops so low that I don’t get a reading on the meter.

I have the battery charging and will see how it reads in the morning. My small charger has an output of 1.25 amps. Can anyone tell me how long it should take to get my 850 amp battery up to full charge? If I understood electricity a little better I could do the math.

Brian Carlton · #9 01-18-2009, 10:43 AM

Quote:

Originally Posted by RML

I have the battery charging and will see how it reads in the morning. My small charger has an output of 1.25 amps. Can anyone tell me how long it should take to get my 850 amp battery up to full charge? If I understood electricity a little better I could do the math.

When one of the batteries needs a recharge due to sitting too long, my 6A charger takes the better part of 24 hours to bring it back to full charge.'

If you've only got 1.5A, I'd say that you're going to need the better part of four days to get it fully charged. It's a fine way to do it........but, you need a lot of time.

nickofoxford · #10 01-18-2009, 12:24 PM

Quote:

Originally Posted by Brian Carlton

When one of the batteries needs a recharge due to sitting too long, my 6A charger takes the better part of 24 hours to bring it back to full charge.'

If you've only got 1.5A, I'd say that you're going to need the better part of four days to get it fully charged. It's a fine way to do it........but, you need a lot of time.

Correct, another interesting thing about this is that batteries prefer slow charging to fully absorb the amperage you are feeding them. This is similar to the principal involved in dropping a socket wrench across the terminals and quickly picking it up, the battery will still read full charge after that.

When you hit a battery with 25 amps for 30 mins or so it will charge it, but your amps will dissipate faster than slow roasting it with 2 amps overnight.

Another part of this is that, as mentioned, you don't get a thorough heating byproduct from the charging cycle itself, and you still have a 32* battery in the middle. Compare this to microwaving a roast on high for 5 mins for the 25amp charge vs. cooking said roast on low for an hour which would represent the effect of the the 2amp overnight charge cycle.

This is more important during cold weather situations when you need every last cold cranking amp for as long as possible.

Jeremy5848 · #11 01-18-2009, 02:22 PM

Excellent point. In cold weather, a trickle charger on the battery overnight may be as important as a block heater. I've seen articles that say a battery loses half (or more?) of its capacity at 32F. The trickle charger not only keeps the charge up but the waste heat from the charging process keeps it a little warmer.