As you can see, each 8-D battery is like 3 car batteries. I have two 8-D batteries, plus a car battery dedicated to the starter for the diesal engine. I charged the new batteries today and just took the shore power off line a few mintes ago to see how they hold a charge overnight. A few days ago I was at the point where I could barely make it from evening to morning without running the engine or the generator (actually I was already developing electric use procedures to get me pretty easily through the night, but they excluded computer, tv, or a lot of light use. These new big boys should last a few days before needing recharging. We'll see.