Opel astra H 1.6 16v 2006 battery and check engine light

I have an Astra H 2006 1.6 16V, and battery light and “check engine light” came on so I took it to the mechanic (in Sweden). They said it was an alternator problem (which I also thought to be the issue since I used a voltmeter and recorded 11 V on the battery with the engine at idle), they changed the alternator and everything seemed fine for a few hours.

Then the two lights came on again and now a strange thing happens: if I measure the voltage on the battery it gives around 10.3 V, but in the “secret” menu on the screen it shows 14.6V with the engine running, and about 11V with the engine off. Furthermore, it also seems to misfire (rpm does not stay constant, but wiggles) at around 2200 rpm in all gears (very noticeable in 5th gear when I set the cruise control to 80kmh).

The fault codes found with the pedal test are:
030100
030200
030300
030400
031300
031400
062104
111505

Does anybody have an idea of what’s causing these issues?

Thanks in advance!