This is normal that you have low battery voltage 12.5V at rest. This is Nissan’s intention to cope with EURO emission standard, at the expense of battery life. IPDM controls the alternator (see 1st page of this thread) in a way that the battery is constantly undercharged. There is a workaround to av...

Disconnect a cable connector from back of the alternator and measure voltage on the battery whether it raise to 14.6V

I guess alternator was OK, they just thought it was faulty, so replaced it but the problem still persists. Most importantly you paid for a new part and labor.
Bring it back and tell them they didn’t fix it so you want to have your original alternator back in the car.

It’s quite rare that alternator fails

@Madmaus would you like to sell the sub?

Then you don’t need to connect AM at all, DAB is powered through the signal cable

What resistors you used and which wires you soldered them to before adding the shrink tubing. This would be much appreciated. Thanx! :) Sure, these are not resistors, but inductance (SMCC-472J-02 ) which ensures that AM signal is not attenuated by +12V power that supplies AM preamp in the shark fin...

Not the fender, but the bumper

If you stand in front of the car, they are positioned behind a bumper on the right hand side between headlight and fog light. There is no access, unless you remove the bumper which isn’t hard to do as well.

Just to update the thread, I fixed the problem with poor DAB/DAB+ reception by this upgrade: viewtopic.php?f=22&t=12477