A circuit assembly for forming and testing batteries connected in parallel and in series includes a parallel test management device (PTMD) that connects to each battery and includes a main relay and a current transducer in series and an auxiliary relay in series with a current limiting resistor, which are parallel to the main relay. Parallel battery groups are formed by connecting multiple PTMD-battery combinations and a voltage equalizer in parallel. Multiple parallel battery groups are connected in series. A battery testing system (BTS) connects to the battery groups. The equalizers and the BTS pass current through the batteries simultaneously. The current through batteries and the voltage drop across the current transducer are about zero at the end of charge and discharge.