We were lucky. One cell pulled the other 6 down in parallel. As a result, too little voltage in one bank on the balancer and battery was no longer usable
Repair was successful.
The error was gone.
Replaced one cell and all voltages are back to normal.
Electronics took a while to relearn.
Despite being fully charged, it had to be charged for a long time in order to be fully displayed again.
And don't be afraid of the volts. 100V You don't...