I have the Blue Seas Automatic Charging Relay (ACR) set-up which isolates the starting battery from the house battery if either battery drops below 12.5 volts (I think). I also use a Guest three stage smart trickle charger which is only unplugged when the boat leaves the dock. Two to three times a year, I also check, with a hydrometer, the gravity level (charging state) of the acid in each cell of the two group 27's I have. Distilled water goes in where needed. Lastly, I have a T8 kicker that will get me home if for some reason I can't start my F225 with both batteries combined (though it might take a while depending on where I am when the failure occurs).
All of that said - I will probably change out my batteries after the third or fourth year of usage but time will tell. So far, I have two years of usage on my batteries and the hydrometer says they're perfect.