Nissan Qashqai alternator?

Question related to nissan Qashqai 1.6 dci 2012.
If someone can explain to me the operation of the alternator?
When I start my nissan at low temperatures, for example around -4, when the car starts, I have fluctuations in the battery voltage! It goes from 12.5 to 14.4 volts, this state changes approximately in about 10 minutes, tested with the lights on or without them, there is no difference, until the engine reaches operating temperature... with such operation, the alternator is very heats up to over 100 degrees, after these fluctuations stop, the voltage stabilizes at 14.4 V, and the alternator temperature drops to the normal temperature. and they don't start anymore) ..
Changed another alternator but it still does the same thing
.. it doesn't light up any errors, the lamp works well, everything is fine in the diagnostics..
I wonder if this is normal? Is there something else that periodically turns on and off and puts a load on the battery?? Except engine heaters!!!
The alternator is a Mitsubishi 150 amp!!