The 721 is offered as a replacement switch for the commonly used battery selector switch. BEP Marine recommends isolated battery systems (ie separate battery switch for each battery bank) as outlined with our distribution clusters. The 721 offers a simple and economic way of switching from one battery bank to another and includes an emergency parallel position. Please note this set up does not protect electronics from harmful engine starting spikes. (Continuous Rating Between Common & B1+B2 500 Amps DC)