Secondary Cell System

The present invention provides a high reliability secondary cell system in which a power supply is multiplexed without using a lead storage battery. This secondary cell system has two or more battery groups comprising a plurality of cells connected in series, each of the battery groups is connected in parallel. Disposed in each battery group are open/close switches that disconnect the battery group from a circuit of the secondary cell system This secondary cell system can comprise an active balancer connected in parallel with the battery groups