in cold temperatures lead acid batteries have higher internal resistance (its also related to why the cold cranking amps is way lower than rated cranking amps)
because of this you need a higher voltage to overcome the resistance and make sure that the battery is fully charged.
the PCM's nowadays typically control the alternator field and the managment strategy also uses data from the IAT/outside air temp sensors as well as battery voltage vs pcm voltage (on board diagnostics and quadrivers let the pcm sense the system voltage drop while under the varius loads as well as the current draw of certain systems.
i believe the upper limit that is acceptable is 15.9 or 16.2v
its fine.
