Many thanks for your opinion. It is not economically feasible to import from CP Euro. The shop is more than happy to replace for free. They have done much work for me in the past and is on my trusted list of shops. I will check the connections as it was a one time occurrence, and replace the alternator if required.

If your handy with work get a new regulator , it’s about an hour and a half job . That’s what goes bad on mb alternators . Mine lasted 80,000 miles . Get a name brand German or a MB unit . 80-110$ . Putting on another used one is not the way to go.

Well, turns out I'm totally rwong on the original battery life.
I took the battery top cover off to check the challenge of removing and installing a new battery (haven't bought one yet).

I noticed a sticker on the battery that reads: "4 / 17", so April 2017. So, not 11 years old, but 8 years old. But still, that's a long life.
....
Also been shopping at Harbor Freight. The battery load tester is still a bargain at $18.00 (CenTech).

I was also looking at the portable jump starters: $70.00 for a starter / compressor combo (CenTech also)

However, I also noticed a Lithium-Ion jump starter for $90.00. This portable jump starter will fit in the glove box!
Might be worth the extra $20. (super capacitor jump starters are higher priced).

I doubt this behavior is protective. More likely the fan speed was changing in concert with the alternator coming on and off line. Get a $5 voltmeter you can plug into the cigar lighter and see if the voltage doesn't fluctuate in time with the fan speed.

So, @Odd Piggy ... dumb question on my part. You state above that a voltage drop below 10.8v indicates a new battery (per MB).

I ran a Load test today (bought an analog load tester) .. the start volts was about 12.5v. Then I pressed Load, and it hits 10.8v after a few seconds, then stayed there for the remainder of the Load (15 seconds). After 10 minutes resting, tester showed 12.4v.

So, is this Load tester more accurate than the "start the engine test with multimeter in volt mode", which showed volts drop down to 9.7v ????
Or is the "start engine" more stressful on battery and a better "real world" test ?

Ultimately, ae we still at, "I recommend a new battery" ?? 😀

I have what appears to be the same tester. It doesn't put as great a load on the battery a the starter does, so you should expect higher numbers. Also, your "start test" depends on a lot of conditions, like temperature and ease of starting for your vehicle. You will get a much lower reading at zero degrees F with 100K miles on your spark plugs than on a summer afternoon in a car recently tuned.

If the needle settles at a constant reading for the duration of the test, and the CCA indicated is equal to or greater than the battery's rating, then I would not replace it.

All that said, if it's 8 years old it doesn't owe you anything.

I had a "no start" after a cold night a few years back. The engine cranked over fine, so I was surprised when the AAA jump box fired it right up. It was a MB battery, only 4 years old. (IIRC - the whole story is posted somewhere). Anyhow, I bought an Odyssey battery from FCP Euro and haven't had an issue in the two years since, and it's been a lot colder, too.

Hi @John CC ... thanks for the details!!
My new Load tester is from Harbor Freight, cost $19.00 USD. It's rated as a 100 amp load.

I zoomed in on my photo in previous post, and the Load needle is resting just on the border of 800 CCA, which is what is written on the battery's sticker.

Yea, it's been at least 70°F daily, tomorrow will be 80°F. It'll get worse after March - our summers last about 9 months 😀

Not dumb - as batteries get old, their internal resistance goes up. The higher it goes, the more the battery works against itself when turning the starter. On-vehicle testers test the battery against a fairly low resistance. Mine uses ¼ Ohm for a 50 Amp load test. The starter has a much lower resistance 0.03 Ohm. So the starter is much harder on the battery than the tester. @MBKLUE has a thread where he shows the 400 Amp carbon pile tester that can approximate a starter. I have a bench tester in storage with four 0.2 Ohm wire wound ceramic resistors in parallel for 0.05 Ohm and 250 Amps. It’s not quite as good as the carbon pile. Those bench testers aren’t used often because they require the battery to be out of the car, they’re bulky, and they get extremely hot. Mercedes uses an expensive Midtronics tester that does some fancy math to back calculate the health of the battery. Then they do the starter test anyway and look for 10.8 V.
Your battery is getting old. You can wait until it just doesn’t start the GLK one day. It’s your call. I’m not quite as conservative as Mercedes, but I don’t want one of my drivers to be out somewhere and not be able to start.

Okay, you talked me into it. I yanked the battery out this morn and went to Walley World and got an EverStart Platinum - compared side-by-side, it's an exact match.

Buying it saved me $45 compared to the Duralast (even with a 10% Veteran discount for Duralast - Walmart does not do the discount). Plus, the Duralast has a 3 year warranty... the EverStart has 4 years.

Next task ... to install the EverStart soon.

hopefully not three years later...

Both Duralast and Everstart are made by Johnson Controls.

Nope ... battery now installated and on trickle charger to top it off. I switched the key to Run (no start), and all looks fine ... when charger blinks, I'll go for a ride.

Appreciate everyone who tolerated me 👍

Yea, it is soooo confusing with all the buyouts and such. I read that Duralast and DieHard were built by Johnson, but they sold off business to Clarios.

Recent rumor is that Clarios manufactures Duralast, Varta, and ACDelco batteries.

I've also read: Johnson makes EverStart batteries for Walmart. Johnson Controls also makes other brands of lead-acid batteries, including Continental, OPTIMA, Heliar, LTH, Delkor, and VARTA.

And yet they've sold off some of their battery business. 🤦

Too confusing for my long retired mind 👍

Wow! I should be in sales (I was for a few years).

The WM EverStart tested well against the MB Varta.

Don’t forget to put the hood into the vertical service position. With the GLK battery in the back corner that makes getting 50 pounds into place easier.