Hi andi, did you try measuring the voltage of the new battery just in case it is bad too? I hope you have a multimeter.
I would not imagine this to be related to the operating system but perhaps you may want to try a different image or operating system altogether. It may help to try a BIOS recovery as well.
I wonder if anything else changed in your hardware that could have caused this.
the new battery is fine and even the old one is still good. I also tried to flash the BIOS again, with no effect.
Finally I got the problem solved by booting Ubuntu 14.04 from an USB stick. After rebooting into the BIOS I recognized the clock now running again
Since then everything seems to work normally again.
Does this make any sense to you?
I am glad you got it working.
It did not make any sense first but now I suspect it is related to UTC vs the local time (GMT) configuration. It seems to be a common issue.