Battery Damage: Sudden Total Failure!

Hi,
Last week, I drove 700 km on the highway with my brother and his Golf 4, which has an ALH engine, and we were often driving at full speed.
The next day, he put the motor through a demanding test with a significant load change.
Then the loader broke down.
He was rambling and babbling, completely incoherent!
The mechanic said that the loader was in a terrible state when he took it apart, completely destroyed!

A load shedding event in itself isn't particularly unusual, but why did it happen after this specific load change?
Previously, the car was working perfectly.

Is there a possible explanation for this?

Sure, here is the translation of the text from German to English:

'MFG' is an abbreviation for 'mit freundlichen Grüßen,' which means 'best regards' or 'sincerely.' It is commonly used in German-language emails and letters.

One thing that can damage a turbocharger is not letting it cool down properly after a long, fast drive on the highway. Due to the high temperatures of the turbo and the lack of oil flow, carbon deposits can form, which can be eroded by the high rotational speed of the turbocharger.
It's possible that something happened while he was refueling or something, and it was only a matter of time before the turbo completely failed.

We didn't do that either.
The engine always idles.

"When a crack initiates, it requires further stress to transition from a slow crack to a rapid fracture. Therefore, the metal needs energy to separate. I suspect a crack propagation failure. This can only occur with a change in load or a high load. It never happens when the vehicle is off."

Please describe what was broken. If a mechanic told me everything was fine, I would be suspicious – that would be a diagnosis I'd want to run away from.
Let them show the parts. At least.

I'd like to do that too!
Problem: The car is in Heidelberg, but we are back in Kiel!
The old loader will be returned to the parts supplier in HD as part of a trade-in.
I would have liked to have seen the loader too!
The LLK (presumably a technical term) must also be expanded and flushed.
We got the charger for €500, which is €200 more than what VW charges.
Everything costs around €1000-€1100, and that's right before Christmas, which is a nice thing.

What surprised me was that a charger failure like this doesn't usually give any prior warning.

Sure, here is the translation of the text from German to English:

'MFG' is an abbreviation for 'mit freundlichen Grüßen,' which means 'best regards' or 'sincerely.' It is commonly used in German-language emails and letters.

The entire charge air duct should be cleaned, as, depending on the type of damage, small fragments may be present everywhere, which could later cause major problems.