For your needs. that is the way to go. Yes, the deep cycle batteries have the power to drive the starter motor. I have always suscribed to the policy of using one battery at a time and keeping the 2nd one fresh as a backup for starting the engine. I will alternate from Battery 1 and 2 on different outings to exercise both. Battery capacity and loads are just one side of the equation you also need to look at your recharging options and capacity. We do a few long trips a year (10+ days) and I don't recall ever starting a day without freshly (90%+) charged batteries. My recharging options are limited to 1) 55 amp engine alternator 2) Marina shorepower to drive 40 amp charger 3) Honda eu2000 generator to drive 40 amp charger. Mind you we run 12V refrigeration. I shy away from running the diesel or the generator exclusively for recharging batteries, it usually comes as a byproduct of motorsailing to maintain speed or running the air conditioner for comfort. While sailing we will cycle the refrigerator one hour ON and two hours OFF. When motoring you can direct the charge to the selected battery via the switch and will direct the alternator charge to battery in use that day. I would recommend you perform a power survey so you may know on the average what are your power requiremnts in amps per 24 hour period. Knowing that and the capacity of your batteries in amps it makes it easy to schedule recharging. For battery longevity it is not recommended that a battery be discharged beyond 50% of its capacity but if you occasionally need to go beyond that threshold it will not cause that much harm. I consider batteries expendable and as much as I like to protect them I will not hesitate to use them to their utmost capacity if the situation warranted it. One beauty about lead acid batteries is that you can easily find replacemnts at reasonable prices in most "port o' call".