Marine batteries, their design, use, and charge/discharge abilities, have been a subject of intense interest within the recreational marine industry for decades. I clearly recall a meeting many years ago, when I worked as a boatyard electrician. I sat in the yard managers office with the manager and one of our long-time customers, a fastidious naval architect who had recently completed a roundtrip passage from New England to Bermuda aboard his 40-foot sloop as part of an organized race. In his hand he had a sheaf of papers which contained neatly written columns recording battery voltages, amperes being used, and the time that each reading was taken, which was roughly hourly, as well as an indication of when and how long the engine was used for charging purposes. He was less than content with the ability of his house battery bank to provide for the modest electrical needs of the vessel. It was equipped, of course, with cabin and navigation lights, communication equipment and radar (the latter only being used occasionally at night), as well as a few other small accessories. Even by the standards of the time, the late 80s, it was an electrically simple boat, yet, the batteries could keep up with its needs.