The Blue Sea Systems ADD-A-BATTERY is as simple to operate as an ON-OFF switch, yet effectively manages the switching and charging of two batteries from a single charge source. The Add-A-Battery provides a Dual Circuit Plus™ Battery Switch and an Automatic Charging Relay. These components simplify switching and automate charging, so that all you have to do is turn the battery switch ON when you arrive and OFF when you leave. Features: Isolates engine & house circuits Combines batteries for emergency starting Tin-plated copper studs for maximum conductivity & corrosion resistance Automatically combines batteries during charging Isolates batteries during engine cranking and when not charging Shares the charge between two batteries more efficiently than a battery isolator Allows efficient dual battery charging without needing regulator adjustment or rewiring Inclusions: 1 x 5511e e-Series Dual Circuit Plus™ Battery Switch 1 x 7610 SI-ACR Automatic Charging Relay - 12/24V DC 120A Specifications: Amperage: 120A Weight: 2.36lb (1.07 kg)