An in-vehicle power supply system includes multiple power cells of identical mechanical size, multiple power pods each holding multiple power cells, and a mechanical transport system to move and exchange power cells with pumps at power cell exchange and charging stations. Each power cell and each power pod includes a control unit and a power converter with a magnetic core. The power cells held by a power pod are arranged parallel to each other and coupled to the power pod by magnetic field coupling. Power is transferred between the power pod and the power cells bidirectionally using magnetic field of different frequencies, and data and commands are communicated between them using magnetic field of another different frequency. Load balancing among power cells within a power pod and among power pods can be achieved. The structure of the power cell exchange and charging stations is also described.