You've had MORE than four alternators replaced ?!?!

First thing ... find a reputable MB mechanic to find the TRUE underlying problem.

Second thing: stop throwing alternators into it - obviously not the problem (unless of course, the alternators installed are cheap-cr@p rebuilt units).

So 5 alternators ? = real dumb since they last forever , only the Regulators go bad at 70-130,000, (if you Hookup a high draw amp)

so I think this is a dumb *** troll.
5 alternators ?
what was voltage drop overnight?
what is battery, how old , what type , what charge at shut off ( after 30 minutes)
what what charge before start up ?

what did amp meter show as discharge overnight ?

who did the alternators ?
who sold you the alalternators?

what type of battery
how did battery load test

how Did battery load test on new battery .

I think this this is a troll. Nobody puts in ( 5 alternators ) unless they’re not mentally correct .

Here is my promised update:

1. I have put a couple of hundred miles on this new battery (small town) and nothing has stopped working or started working since the install. I have not had any aborant milage readings like I had with the old Aux Battery when it failed.

2. I used my scan tool and there were no codes. The battery read 100% charge. The odd thing is the Eco Stop/Start does not seem to be kicking in but that annoying function was not kicking in before the new install. The button's green light is still on so OK?

3. I did not cover this before but when you use the CTX14-BS code in Google or Amazon for instance you get a list of AGM batteries from a number of manufacturers.
a. While they are all AGM replacements they are NOT all the same dimensions. They are close (e.g., +/- 1/8") but with the battery holder fittment being so close I opted for one closet to OEM.
b. Your search may also give you a YTX14-BS. That is an older model and the CTX14-BS is its replacement.

That's all Folks

The Aux. battery had nothing to do with your mileage readings. As others have mentioned, it's there for Eco Start/Stop reasons. I drove around for months with no Aux. battery installed (it would no longer hold a full charge and I removed it). Had no effect on anything. Certain parameters must be met before the Eco Start/Stop begins to function. If those parameters have not been met the Start/Stop will not function. The green light being on only means you have not manually turned off the Start/Stop "functionality possibility."

THANKS for the follow up !!

1. When my Aux went bad (got the Aux Failed for quite a while), I had no issues with mileage readings.
2. When I installed the new Aux, ECO worked immediately as it should (unfortunately!).
3. a. I drove up to the local O'Reilly Auto Parts, removed the battery - we compared to the new one, and it matched on all sides - direct drop in.
b. I'll go look at what the new one's part number is.

Sidenote: I always buy my batteries from a US auto parts chain (local store), cause as I said, I got to inspect the new battery on the spot, before purchase. 5 minutes after I walked out, I had the new Aux installed.
Also, if something goes rwong, an exchange can happen right now - no waiting for a new shipment and the hassle of shipping old one back.

Thanks for the reaserch and feedback.

I don't have any love for the Eco function so as long as it is not throwing codes I'm good

Looking at possible causes for some of the things that have happened over the years I believe it comes down to the software codes/coders not doing a good job of integrating patches/upgrades. I also believe some of it is to manufacture issues to drive revenue. Here are 2 examples:
1. In 2016 I had a transmission CU fault and the MB dealer installed an "update patch" that I researched and found it was common to what's used in the 500s (don't remember the specific models but MB dealer mechs know what their doing, right). It worked fine so I did not think much about it until about a year later. If the car was left in the hot Florida summer sun the RPMs ran much higher for short period of time when I started it up. I checked the forum and the 500s had the same issue under the same conditions. The solution don't let it sit in the sun and get hot, and the problem goes away.
2. Wheel sensor(s) went out a couple of months apart. Both instances the the dash lite up like the wrath of God had been unleashed and it went into limp mode. Why limp mode? It could easily scare the **** out of someone and cause an accident (I lived in Dallas for 6 years) or have some (vulnerable) individual or family have pull off the road in some dangerous area (I ended up in East St Louis going to visit the arch and that is not a place you want to drive through let alone stop)?

So I try to stay away from the MB dealer as much as possible, source things, that meet MB specs., locally if I can and do as much of the maintenance as I can and want to. Just like you do apparently. This Aux Battery purchase was kind of an experiment I bought my main battery from the local PEP Boys.

Why limp home mode? To help protect your vehicle and you. You lost 25% wheel rotational speed data (or 50% data lost at one end of the vehicle). That data is used for ABS, ESP, 4MATIC drive adjustment, possibly transmission shift points, tire pressure warning for some markets etc. Limp home mode, obviously, does not mean you must stop immediately or even in the next few miles.

I had my original battery lasted for about 10 years 9 months and my garage recommended to change it due to potential for failure in cold weather. It was working and based on battery check condition , I decided to change it. I have changed Energizer AGM H7 battery purchased with 5 years warranty ( no replacement cost within 5 years ) from Costco. Battery cost was $ 280 + tax. No issues so far. Original battery from MB dealer quoted $460+tax. Any recommendation or comments .

My 2014 (also a 250) is on battery #3. The first two were OEM. I opted for an Odyssey battery for $250 from FCP Euro with a lifetime warranty. Time will tell...

My original OEM /MB main battery was made by Verta in Germany which lasted 10 years 9 months. I learned that, Verta was purchased by Energizer about 10 years ago.

My 2014 OE battery lasted almost 10 years, being a Dec 2013 build. I replaced it a few months ago with a NAPA unit (part# 9AGM94R) for $215. It has a 3-year replacement warranty.

My main battery cost in Canadian $ 280 ( US $215 about CD $ 292) with 5 years replacement warranty and 100 months prorated warranty from Energizer / Costco.

@Roger Rajah, @andreigbs, @John CC ...

I might be rwong, but it appears this is drifting from an "AUX battery" thread to a "MAIN battery replaced ..."
Starting at post #33, with a title as "2013 GLK 250 Main Battery".

I replaced my AUX Battery not long ago, which I purchased at O'Reilly Auto Parts and it was about $125 USD.
Are these batteries in the last 3-4 Replies (in the $200+ range) an AUX battery or the MAIN battery??

You're right, we've wandered off the original topic; apologies.

I have no AUX battery in my GLK250, no start/stop system.

Not my fault! I just responded to post 33....

No aux battery in my GLK. I understand there's one in the GLS. When It goes bad I'll be back!

I'm certainly not trying to be an Admin just asking what happened to the thread

We have a 2014 GLK350 Base, and it has an Aux.

Either that, or our main battery lives in the trunk, about 6" long, and I can hold it in the palm of one hand

I was referring to my GLK250's main battery replacement only.

Do you have eco start/stop? I don't.

The Gassers (at least with some or all of the face-lift model) have Eco Start/Stop to lower the overall fuel consumption to meet certain requirements/averages. The Diesels don't need that extra little reduction because they already have stupid low fuel consumption, from what I've read - he writes with envy...

Interesting. I drove a ML350 with a V6 Diesel and it did have start/stop.

You're spot-on ... our 2014 GLK350 Base (gas) has Eco, which we abhor. First physical reaction getting into the GLK and crank it on, is to hit the Eco button OFF.

It's horribly annoying for the engine to cut off at stop lights/etc. My 1st gut reaction is, "cr@p, the engine died, now what". When the Aux battery died recently, I thought, "oh good, now don't have to worry about Eco". rwong. Now you get "Aux battery bad" messages until you replace it. Eco = bad feature.

Maybe it had that because of the larger engine and greater size and weight compared to the GLK. I would imagine it was noticeably more thirsty than the Diesel GLK.

I don't have echo start/ stop, but when it is in idle at signal light gear shift go to parking mode ( engine runs without stop- P high lighted in my display ) . I have auxiliary battery in my GLK250 not replaced yet from original OEM. It is about 10 years 9 months old.

Okay, that seems VERY suspicious to me ... I would NEVER want a vehicle that automagically shifts into Park all by itself !!

And WHY a vehicle would do that as you stop at a stop light or stop sign is beyond me.


HOWEVER, I will admit, when I pull out of our driveway (about 100 yards long ), I usually then backup to the mailbox to check for mail.
If I OPEN the door WITHOUT first shifting from Reverse (or Drive) to Park, the GLK shifts into Park (I guess for safety reasons).


If yours is doing that, and you're NOT OPENING a door, you better get it checked out !!

it is a display change to P not a full gear shift and when I rease my break at idle ( at stop in red signal lights) , it automatically move to drive D1 without any issues. This feature is active since when I purchased new from dealership. I believe it is a fuel save option added to my GLK 250 when engine is in idle at stops.