"Voltage at the alternator's contacts is 14.4 and at the battery is 13.6"

That sounds like everything is working as expected. But I think your voltage at the battery is a bit low. Theoretically it should be exactly the same as measured at the alternator, with only a slight loss due to connection resistances at Alternator B+ => Starter => Battery positive.

If you haven't yet disconnected and cleaned the large red wire connction at the starter, you might want to do it. I just measured my '93 940 (100A Denso) right after a cold start and got these values:

14.57-9 at alternator B+ (fluctuating at 100ths position)
14.53 at battery + (steady reading)

And with meter black lead on Battery + and red lead on alternator B+,
the total "drop" (loss) measured .06 volts (steady).
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.