wjcandee

I can't emphasize enough how much of a role that the battery in the W211 has in stabilizing the electrical system, and why it's an important thing to consider when evaluating electrical gremlins.

My tale: Recently changed the alternator and the front SAM, the alternator because it died and the SAM because it had a blown rear a/c control (dual valve control) chip. Fixed all my problems. A couple of weeks later, i.e. a week ago, the car started exhibiting a very specific symptom, as follows:

I would start the car after being in the garage all night. Everything fine. I would get out on the local roads to aim for the highway. No problems. Then I would go either 5-10 minutes on the highway to a tunnel, where I would have to stop at some lights before entering, or I would take a different highway route some 35 minutes before exiting and stopping at a light. I would have no issues before this, including when stopping locally after just starting the car. But at the tunnel, or at the exit, the instrument panel lights would reset, kind of as if you would turn the car off and back on, or if the car would start to stall and then catch itself. The a/c would simultaneously click off and right back on. But unlike either of those examples, the engine was just sitting there purring away as normal. After that, and maybe one or two recurrances right thereafter, the car wouldn't do it again until the next day. It seemed to be getting worse each morning (on the last day before repair, it did it while I was accelerating), but otherwise the car was fine.

So the symptom was a reset of something in the electrical system that happened during the normal voltage fluctuation as one approached and stopped at a light, but only after 10-30 minutes of highway driving, and not before and not really after that.

There were a lot of things that could perhaps cause the immediate symptom, including the voltage regulator on my new alternator, or something in my "new" (used) front SAM, but given the unique and repeatable circumstances, my first guess was my 4.5-year-old main battery. I generally keep it well-charged by topping it off every few months with my trickle charger, and also do primarily daily highway driving, which should be sufficient to keep it charged. And indeed, looking at the UB voltage, it appeared to be fine.

So I changed the battery, and it completely solved the problem. No more resets.

So this is just a reminder never to discount the possibility that the battery is involved when diagnosing electrical gremlins. We already know that the electrical system in the W211, and Mercedes generally, is finicky. And we may not think immediately of the battery when it is carrying an appropriate voltage and starts the car effortlessly, and handles the lighting with the engine off flawlessly. But remember what an important role the battery plays in our electrical system of stabilizing that system, and you will consider it more quickly when weird things start happening.

On our W164 two years ago, I was told by a frightened Mrs. that the car started "going crazy" when she was driving home. She said lights were flashing and buzzers buzzing and klaxons sounding and she was petrified driving the last 5 minutes home. She wanted to flatbed it immediately to the dealer, without turning it back on. I thought she was being colorful, so I went out and put the key in the car and turned on the ignition. HOLY CRIKIES! It flashed lights and made sounds that I didn't even know it could! Loud. Disturbing. Yikes! She wasn't exaggerating. Having read something a couple of years before on MB World about this, I calmly (after bailing out of the car immediately) went and bought a new battery and installed it myself (which I recount on another thread with instructions; it's not hard if you know the tricks, but it's time-consuming the first time on the W164). Car immediately went right back to normal.

If you don't just open a beer and call the MB Roadside Assistance guys to come change your battery, here are some thoughts.

$139.99. That's the best price you're gonna get on an AGM battery for the car, and it's an easy DIY replacement on the W211, if you are reasonably-strong and can lift the battery.

Everstart MAXX Platinum and Rural King AGM are the two batteries at that price, if you can find them. Rural King has free shipping on their H8/Group 49/L5 AGM battery, but it will take a few days to get it, unless you live in the Midwest and can go into the store. The Everstart Platinum at WalMart, if available (which it usually isn't) is a Johnson Controls battery. The $139.99 Rural King AGM is made by Exide, and is identical to their $220 AGM battery in that size.

Looking locally, the Group 49 Advanced Gold AGM at Sears is a nice battery, but is about $20 more expensive right now, even on sale. Perhaps the best deal locally is the Advance Auto Parts battery, which is now what I have in both cars. If you get their H8/Group 49 (same thing) Autocraft Platinum AGM battery, you can order it online and pick up in the store. If you take the 25 percent discount available right now for online ordering, it cuts the price to $144, which is what I paid. That's a big savings over the Interstates and East Penns that a gas station will sell you for a lot more money.

When lugging the battery out of the store last night, I noticed that it was two months old and had a sticker on it that said Made In Germany. It is most-likely a Johnson Controls battery, but I have to say the sticker was reassuring.

Take a look at Pelican Parts, because they have a nice little primer on changing the W211 battery, with photos to show you how to do the trickiest thing, which is to operate the totally-non-intuitive buckle on the fabric strap that helps hold the battery in place. Also, if you have a little magnet on a stick device, one of my favorite tools, it will help you easily extract the bolt that attaches the hold-down-plate after you free it with your 13mm socket extension.

One other pointer: Advance will tell you that the battery is "fully charged". Yeah....no it isn't. It's charged enough for sure, but it isn't fully-charged. It's a 95 amp-hour battery, and it spent over 3 hours on my 10-amp charger (on the AGM setting) before the light turned green. As a matter of very-rough math, that means it was down about a third. That's okay, but given the circumstances, I wanted to install a battery that was truly "fully-charged".

At many stores, Advance will install the battery for free, which is a nice thing. (Mine can't due to local zoning restrictions...grrrr.)

Hope this helps!

TPAbnz

Did you consider the Bosch AGM at Pep Boys?

wjcandee

Good point. I usually mention them as well. These are manufactured by Exide, and so are good batteries. (https://globenewswire.com/news-relea...-Pep-Boys.html) With the current discounts online at Pep Boys, they are about 20 dollars more expensive than the one I got at Advance, and about 25 dollars more expensive than the equivalent Exide that you can get at Rural King.

Of course, Pep Boys does have a solid Price Match policy, so you can probably get their AGM battery for whatever the best price is you could find it somewhere else, if you can show how much you would pay elsewhere.

If the local Pep Boys was closer than Advance was, and was open on Sunday as late as my Advance is, I certainly would have considered the Pep Boys offering when buying a battery last Sunday. One positive: a 4-year warranty on the AGM version, rather than just 3 years for most others these days.

For a lot of folks, the fact that Advance will install it for free and Pep Boys wants 60 bucks or something to put it in the trunk might be a sticking point. Since I'm happy to do it myself, it makes no difference to me.

Redwood415

I have heard this story so many time over. If your battery is more than 6 years old and you are having strange error messages and weird things happening - replace your battery (even if it shows good voltage with a multimeter) Do use a GENUINE Mercedes Varta Battery. so what if you spend $60-$80 more than a discount battery that's supposedly good for foreign cars. Why did you buy a Mercedes if you cant afford genuine OEM parts?


Cheers.

wjcandee

Basically-agreed. I often buy parts from other than the dealer, but I always buy quality. Bosch Alternator, Denso A/C compressor, Egelhof valve, Lemfoerder suspension parts, Pierburg EGR valve, Zimmermann Rotors, Bosch sensors, Bosch Air Injection Pump, Hella Xenon igniters and ballast. I don't always buy the OEM provider's part, but almost always do.

Regarding batteries, Varta is made by Johnson Controls, which makes the batteries sold at Advance Auto Parts. Most likely, the "Made In Germany"-labelled H8/49 Battery I just bought was part of a shipment that otherwise would have gone out with Varta labels on them.