The StartNow automatic starter switch and battery combiner from Charles Industries ($128) is a microprocessor that allows your tender or center console’s main battery to drain without draining the reserve battery too, so you can still start your boat after a long day at the sandbar or fishing the flats. A sensor on the StartNow system automatically detects if the voltage on the main battery is low and activates the second battery to start the engine. Charles Industries, 800-830-6523; www.charlesindustries.com