The output of the alternator is but one factor or source for a charging
current.
We have been cruising for 4 years and can stay in an anchorage for
weeks without starting the main engine (no gen set)
We have 4 x 80W solar panels, AirMarine wind generator and when we are
under sail a tow along generator (.75A/Knot)
The fridge is 12V eutectic with enough insulation around the box for
prolonged tropical cruising.
Even on max demand the alternator never exceeds 75% of max output for
greater than 10 mins.
I guess the lesson we learned was have enough alternative energy
sources to cover most of your day to day needs.
Lyn & Tony
S/V Ambrosia