With waterproof design, suitable for indoor/outdoor or ocean use. Built-in overload, over-current and short circuit protection, very safe to use. UV stabilized nylon housing with rubber splash-proof & tight-fitting front cap. Voltmeter with three digit LED digital display, real time monitor the battery voltage. 2 pole nickel plated brass terminal connectors Mounting screw and labels included, easy to install, can be installed horizontally or vertically. Use on automotive electronic field, electrical devices, most car, truck, buses, SUV, home, boat, camper/RV, ATV, UTV, golf cart, and more electrical devices. Can be used to charge for mobile phones, tablet, GPS, digital cameras, PDAs etc. Specification: Item Color: Black USB Color: Blue USB Input Voltage: DC 12V-24V USB Output Current: 4.2A(2.1A/2.1A) Interface: 2 USB Voltmeter Display Range: 0-35V DC, 10A Voltmeter LED Light Color: Green, Red, Blue (Optional) Voltmeter Mounting Hole: 29mm Switch: Waterproof, ON/OFF, Red light. Cigarette Lighter: 12-24V, 10A Fitment: universal for 12-24V car, boat, marine, RV, truck and etc. Package Included: 1 x Digital Voltmeter 1 x Dual USB Car Charger 1 x Cigarette Lighter 1 x ON-OFF Rocker Toggle Switch 1 x Four Holes Panel 1 x Set of wires