I run my original 26 year old 55 amp Motorola alternator to charge up my 3 group 31 batteries. The batteries feed a 1500 watt inverter that usually just handles the undercounter 110v fridge but also a toaster, microwave, teapot, coffeemaker, tv/vcr, hair dryer, ceramic heater, 110v reading lights (not all at once). It also has to handle all the normal 12v loads of the average trawler. Before I left on a cruise, I called my parts man to order a spare alternator. He talked me out of it. His opinion was that these are robust alternators and that he had not seen many problems with them during in his 20 years in the business. If I needed an alternator during the cruise, he would "overnight" one to me. He was right; I never needed it. The 6 to 8 hours of daily running always topped up my batteries as far as I know. Every couple of days, we overnighted in a marina and the regular battery charger was brought on line. The inverter and charger are separate units by choice. This type of simple setup works if you stick within reasonable limits. Al Johnson 34' Marine Trader "Angelina"