The Add-A-Battery includes 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:Dual Circuit Plus Battery Switch:- Simplifies switching- Isolates engine and house circuits- Combines batteries for emergency starting- Tin-plated copper studs for maximum conductivity and corrosion resistanceACR Automatic Charging Relay:- 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 rewiringSpecifications:- Amperage: 120A- Weight: 2.36lb (1.07 kg)