Insert Car cigarette lighter socket, can display battery voltage;  Health voltage: 12~14.5V; Error: 1% ( +/- 1); Compact and convenient to use; Super brightness 3-digit nixie tube display; Can monitor storage battery voltage constantly, extend the using life; Operating voltage: 4~30V; 12~24V; Healthy of the battery: 14.4V~14.8V Good; 13.4V~14.4V Good; 13.2V~13.4V Not bad; 12.8V~13.2V Check; 11.9V~12.8V Good; 11.6V~11.9V Check; 0~11.6V Bad