Marine SOLENOID ADD a Battery Kit - 65A On-Off Switch. Adding a second battery to the electrical system prevents the unintended discharge of the engine start battery. Blue Sea Systems popular Add-A-Battery kit was primarily designed for boats with alternator output of 120A or less. When installed, the Add-A-Battery isolates the start battery from the house loads which prevents the discharge of the start battery. The Add-A-Battery offers a simple way to control the charging and battery switching of two battery banks. The E-Series Dual Circuit Plus? Battery Switch simplifies the switching while the SI-ACR automates charging between two batteries.