The pictures were taken by the homeowner (a professional electrician) - he posted them on a German language forum.
Here's a google translate of his forum post:
Good morning,
The trigger was the middle battery of the 3. A BASEN that had been running for 1.5 years. Without making a binding...
The investigation has come to an initial conclusion. It looks likely that it one of the server rack batteries that caused the blast after all..:
Interesting fact: this is the middle battery - the ones below and above appear to be unaffected, and were still charged (these contained prismatic...
