Most "marine" batteries are sort of a hybrid starting and deep-cycle battery. I think they're essentially a starting battery with thicker plates. They're buil

Most "marine" batteries are sort of a hybrid starting and deep-cycle battery. I think they're essentially a starting battery with thicker plates. They're built that way because, on a boat, you need a lot of current to start the engines but you also use the batteries as your sole 'housekeeping' power source from time to time (particularly on sailboats when the engine isn't running). Real deep-cycle batteries would be better, but they're more expensive. Something like this http://www.usbattery.com/usb_solar_p1.html http://www.usbattery.com/usb_solar_p1.html would probably be optimal; it's designed for use in alternative energy systems where you charge during the day from solar cells and then discharge during the night. Very heavy plates. A cheaper alternative, which I've seen some people use in UPS systems, are wheelchair or golf cart batteries. Both of them are true deep-cycle designs, made for sustained loads.