Mercury - Voltmeter 8-18V Electrical System Monitoring Black Face Black Bezel 79-8M6020033. OverviewThis 8-18V voltmeter gives you a steady, no-nonsense read on the boat's electrical system. The needle settles quickly, even when the water's lumpy, so you get a true sense of what the battery and charging system are doing. It's one of those gauges you end up checking without thinking-just a quick glance to make sure everything feels normal. Simple, reliable, and easy to live with on long days.. Ke