W210 Battery Charge Indicator Question - PeachParts Mercedes-Benz Forum

shertex · #1 01-06-2015, 09:35 AM

If the reason for the battery charge indicator (my 98 E300) coming on at start up is a weak battery, what's the threshold in terms of the weakness of the battery that trips the indicator?

We were out of town for ten days, then didn't drive the car much in the subsequent week, and it was 16F this morning. I'll get it fully charged in preparation for -2F Thursday morning!

KarTek · #2 01-06-2015, 01:42 PM

I've never had the indicator come on for a weak battery but I have had warnings for a low output on the alternator which turned out to be the overrun clutch on the alternator going bad.

The situation resolved itself so it may have been some sort of contamination that burned off.

Jeremy5848 · #3 01-06-2015, 02:15 PM

I don't know how smart the electronic systems are in the 1998 cars so I won't put foot into mouth and say the car can't detect a "low" state of battery charge. Most "battery" or "charge" lights simply detect whether the charging system is generating current to feed the various loads and re-charge the battery. My '96 E300D does only that; who can say whether the 1998 is better/advanced?

The way to detect a low battery charge, apart from measuring the specific gravity of the electrolyte (and that's hard with, for example, an AGM battery), is to put a known load on the battery and measure the battery voltage. For example, a fresh battery should stay above 12 Volts for a few minutes even with the headlights turned on. (I've not done my own tests so I don't have specific numbers for you.)

There are commercial testers to do just that; I bought one from Harbor Freight that clips onto the battery terminals and gives you some quality numbers. The part number is Item #66892 for the one I have; usually $80 in their on line catalog and occasionally on sale for less (or use the coupon good for 20% off). Other brands and options abound. YMMV.

Jeremy

shertex · #4 01-06-2015, 02:35 PM

Thanks. I'm sure I'm simply mistaken that the indicator would reflect a weak battery. In any event, the indicator didn't come back on after a cleared it. Hoping it's just a bitter-cold glitch. We'll see.

KarTek · #5 01-06-2015, 02:37 PM

When mine was failing, the information display literally turned red (not the normal happy amber) and there was an icon of a battery right in the middle with nothing else.

shertex · #6 01-06-2015, 03:00 PM

Quote:

Originally Posted by KarTek

When mine was failing, the information display literally turned red (not the normal happy amber) and there was an icon of a battery right in the middle with nothing else.

Ominous.

shertex · #7 01-08-2015, 10:20 AM

Same thing happened this morning. Very cold (3F), started car and battery charge indicator came on briefly then disappeared by itself. Drove without incident.

shertex · #8 01-08-2015, 10:22 AM

It also very briefly turned red instead of amber.

So.....I'm wondering whether this is simply some cold whether glitch or if this is the alternator in the early stages of failing.

dieselbenz1 · #9 01-08-2015, 10:34 AM

Sounds to me like your voltage regulator is on its way out I'd be ordering a replacement. Or you could wait a month or so like I did and need to get a boost before ordering it.

Jeremy5848 · #10 01-08-2015, 10:37 AM

Quote:

Originally Posted by dieselbenz1

Sounds to me like your voltage regulator is on its way out I'd be ordering a replacement. Or you could wait a month or so like I did and need to get a boost before ordering it.

That's a good point. OP, when was the voltage regulator last replaced? It's an easy DIY job and the regulator is not expensive ($50?). If the old one is still semi-good (brushes not totally worn) you can keep it as an emergency spare. Might as well do the job while you've got control of the circumstances, not on the side of the road in the snow.

shertex · #11 01-08-2015, 10:42 AM

To the best of my knowledge, both the alternator and the voltage regulator are original. Looks like I can pick up Bosch VR for $27.

So I gather that, since it's original, might as well just replace it and see where things stand?

Jeremy5848 · #12 01-08-2015, 12:18 PM

Quote:

Originally Posted by shertex

To the best of my knowledge, both the alternator and the voltage regulator are original. Looks like I can pick up Bosch VR for $27.

So I gather that, since it's original, might as well just replace it and see where things stand?

There are many advantages to putting in a new VR proactively
* You learn how to do the job before you have to do it on the side of the road;
* You get to do the job under controlled conditions (Murphy's Law of Thermodynamics—"things get worse under pressure") and at a time of your choosing;
* The car gets a brand-new VR, no more worries for many years and miles;
* The old VR, if still good, can be stashed in the car as an emergency spare.

While you're in there, examine the alternator slip rings on which the brushes ride. Although the brushes do most of the wearing, the slip rings wear too, gradually becoming "trenches." Eventually they too will fail.

shertex · #13 01-08-2015, 01:13 PM

Quote:

Originally Posted by Jeremy5848

There are many advantages to putting in a new VR proactively
* You learn how to do the job before you have to do it on the side of the road;
* You get to do the job under controlled conditions (Murphy's Law of Thermodynamics—"things get worse under pressure") and at a time of your choosing;
* The car gets a brand-new VR, no more worries for many years and miles;
* The old VR, if still good, can be stashed in the car as an emergency spare.

While you're in there, examine the alternator slip rings on which the brushes ride. Although the brushes do most of the wearing, the slip rings wear too, gradually becoming "trenches." Eventually they too will fail.

Can this be done with the alternator in place or does it have to be removed?

Jeremy5848 · #14 01-08-2015, 02:47 PM

Quote:

Originally Posted by shertex

Can this be done with the alternator in place or does it have to be removed?

You should be able to do it with the alternator in place. If you can get the black plastic cover off of the alternator (3 screws + 3 clips), you can unscrew and remove the regulator. I mention this only because my '95 E300 (similar 606 engine) has coolant pipes running from the thermostat housing to a heat exchanger in the oil pan. These pipes pass just behind the alternator, meaning that I have to remove the alternator before I can take the black plastic cover off. Your turbo-606 has a different oil cooler, I believe, so you should not have a problem.

The "clips" I mention are part of the black plastic cover—use a screwdriver to spread them out and they'll release. Don't pry too hard, they'll snap. Not sure why both are used, the screws alone hold the cover very well.

VW1300 · #15 01-08-2015, 10:06 PM

Shertex, have you used the diagnostic on the climate control panel to check the voltage in the system? I used it to check my '97 shortly after I got my car and discovered my volts were low - new regulator brought things back up to 13.5 V or so.