A padded seat is described that includes a top surface, a bottom surface, a compartment disposed between the top surface and the bottom surface, a closeable opening to fill the compartment with a fluid, a plurality of through holes which pass through the top surface, compartment, and bottom surface, and a non-slip element disposed on the top surface. The read heads include bottom and top magnetic shield layers, a read sensor or magnetically sensitive element between the bottom and top magnetic shield layers, and a side shield assembly formed of magnetically shielding material positioned between the bottom and top magnetic shield layers and adjacent at least a portion of the read sensor. With this, the power storage apparatus identifies a power storage element that has high impedance among the whole and its impedance, and detects and displays deterioration or malfunction through a threshold-value judgment. In preferred embodiments of the invention, at least one of the receivers is replaced by a reflector and at least one of the transmitters also functions as a receiver.