A modular reconfigurable battery system for second life batteries based on cascaded DCDC converters named FlexBat is presented. Compared with conventional systems, the power of each submodule can be controlled individually, increasing the available capacity. Faulty modules can be bypassed, increasing reliability and fault tolerance. The chosen approach is compared in detail with various reconfigurable topologies, as well as other cascaded DCDC converter systems. Furthermore, design, operation and control of the FlexBat system are described. Finally shutting down a faulty battery module is simulated.