The radio plays but nothing shows up on the screen no matter what buttons I press or turn. Its a touchscreen, and things like bluetooth and gps(roadcommander) work fine. The temperature, time, and radio frequency are all 'stuck'.
You are in Denmark, I am in Wisconsin, with failure of my negative battery cable, it was dropping 2.1 volts under any kind of load. And this was the new one, on the old one were using a 1.25 mm larger clamp on it, that is actually intended for the positive terminal.
Its problem was they did not solder the copper tip inserted and crimped into the correct sized negative battery terminal that corroded with bare copper. I soldered that in.
First electronic equipment to act up, was the radio, apparently it needs at least 12 volts to operate properly. Good thing the ECU was working, or I would have had to push my Cruze home.
To test yours, switch on the blower motor, engine can be off, and with a voltmeter, touch one end to the negative battery terminal itself, the other end to where it is grounded. Should read just a small fraction of a volt, like 0.14 volts. Mine was reading 2.1 volts.
Seems like if just one of us has these kinds of problems, with mass production, everyone could have the same exact problem. But don't know until you look and test.