A battery system includes a plurality of battery cells connected in parallel. Each battery cell includes a positive and negative tab. The battery system also includes a plurality of thermal switch devices (e.g., temperature cut off (TCO) or positive temperature coefficient (PTC) devices). Each thermal switch device is electrically coupled to a respective cell. The battery system further includes a rigid-flex circuit board comprising a plurality of rigid regions. Each rigid region is physically and electrically connected to an adjacent rigid region by a respective flexible region. Each rigid region is electrically coupled to respective positive and negative tabs of a respective battery cell. Each thermal switch device prevents abnormal current flow (e.g., by limiting the flow of current at high temperatures) between a first battery cell that is coupled to the thermal switch device and a second battery cell that is adjacent to the first battery cell.