Hey all,
I searched the forum (and 3 others) for several days now and I'm unable to find any posts that would apply to my situation and I've ruled out or tried all of the other solutions. So, I've started a new thread and appreciate any help you could offer on this.

This thread is related to this one- regarding installation of a new alternator and etc.:
143A alternator from 96 S420 in a 96 E300?

The original problem began a couple of months ago when I had a "no start" one morning. I put the battery on a trickle charger to get it charged and started, but saw that that the voltage in the climate control display would not get above 12.1-12.5 volts while driving, and the battery didn't get above low 12 volts. I had to leave it on the trickle charger in battery tending mode just to drive it every week or so. So, before changing parts, I removed the rear seat and hooked up a multimeter to the battery and watched the voltage when starting the car- glowing the plugs dropped the voltage at the battery to 11.5 or less. Cranking the starter dropped it even more- even down into the high 10s. After it started the voltage would stay in the low 11s or high 10s while the glows were running, but after they cut out, it still wasn't charging the battery because the voltage stayed in the low 12v range at the battery. I always noticed that the dome lights and headlights had been somewhat dim since we bought the car.

So, after researching similar problems, and taking the battery in for testing several times and being told it was "good, needs charging" I let the store rapid charge the battery and embarked on the journey to clean all of the ground straps, and replace the big un. More on that here with pics:
W210 ground strap location?

The car now has bright, shiny, tight and squeaky clean ground straps and wires including the one at the passenger side of the rear seat for the battery and a new one at the bell housing to chassis. The car has a brand new 143a alternator that is giving 13+ to 14v on the climate control at 2000-3000 rpm. The battery was even replaced with another one from Advance. (It has an advance battery because last year when it had a "fail to start" and was towed to the shop from the gas station where it died, it was the only local battery they could find for the car. Battery replacement seemed to fix the issue- at least until this same problem appeared 1.5 yrs later as referred to earlier. This "new" battery is wearing a build date sticker of 4/2012)

There is also a brand new serpentine belt and all pulleys are completely clean. There is absolutely no belt squeal.

Prior to cleaning the ground straps, and replacing the alternator with a brand new 143a model, it never gave any sort of "battery charge" light or anything. Now, after all of this (clean grounds, clean pulleys, new serp belt, new alternator, new battery) I'm getting a red "battery charge" display and beep after the glow plugs are glowed, immediately after cranking the starter (which fires right up). After resetting the battery charge light- it stays off the entire time I am driving around. And, as stated earlier- the climate display is showing 13+ to 14volts while driving after the gp's cut out. When I park it and shut it down- the "battery charge" displays again with a "beep." I just went out to the garage and checked the battery voltage at the post under the hood and after sitting for 3 days it's at 12.52 volts. After parking it 3 days ago the battery was at 12.6volts.

Is this symptomatic of another defective battery? Is this a bad positive battery cable? (connectors at both ends are perfectly clean.) The system voltage on the climate control is fine- what could this be? Gaaaaaahhhh!

Any help is appreciated! Thanks- John