The typical construction used for most rechargeable cells is shown here. The two electrodes have a non-conductive separator layer in between them. These three sheets are wrapped in what is referred to as a “spiral wound” type of design. The materials are put into the cylindrical metal housing, and a conductive fluid is poured in to fill the space. The physical design of the case includes a pressure relief valve and positive-temperature-coefficient element which will disconnect the cell in case of extreme high temperatures. When cells are charged and discharged, the internal chemical reactions may result in gas generation inside the housing. In addition, there may be some temperature increase due to ohmic losses or exothermic reactions. The pressure relief valve and PTC prevent continued current flow to the external circuit in case the cell temperature and pressure go too high. In many cases when cell failures have been analyzed, the root cause is often due to small particulate contamination or metal particles that may have punctured the separator causing an internal short. When there is an internal short, disconnecting the cell from the external circuit cannot remove the fault. So, high quality in the manufacturing process is essential to prevent contamination during cell construction. Reliable cell manufacturers will have strict quality control procedures that ensure their cells provide consistent, reliable performance and minimal chance of failure when they leave the factory.