You can try cleaning the ends of your relays, the box is in the front of the battery in the 156. Relays are black cubes with 3 connectors underneath.
I had this problem before, and a battery that was expired 2 years ago (consider we don't have winters here) was not appreciated by the sensitive complex electronics of the Alfa - just like any high-end vehicle. You can test your battery, should read ~12.68 Volts, key off, engine off, at normal temperatures.
Engine on, all accessories off, the potential at the battery should be near 14V. This is basically a test of the alternator as well. With A/C and radio on, it should also be higher than 12.68V ideally..
PS: Correct me if I'm wrong, dudes?