Typical separators used for lead–acid batteries throughout the world are listed in Table 2, together with the battery characteristics. Among these, the leaf-type SPG separator and the pocket-type PE separator are used in Japan according to the battery application, battery usage, and system requirements. The SPG separator is used together with a glass mat in heavy-duty batteries that must have high vibration and temperature durability in vehicles such as buses, trucks and taxis that operate under severe conditions. The PE separator is generally employed in batteries for passenger cars with a light load and is used in about 70% of these batteries. Regarding the background in which the PE separator is widely used: (i) the road conditions in Japan have been improved so that battery vibration during driving has decreased and, accordingly, the requirements for vibration resistance have been reduced; (ii) because the grid has been changed from a conventional cast-type to an expanded-type (calcium alloy) due to popularisation of the MF battery, a separator capable of being shaped into a pocket is needed to prevent loss of active material from the positive plate; (iii) the change from the leaf-type to the pocket-type separator has contributed considerably to an increase in productivity of battery manufacture; (iv) the durability of the PE separator has been greatly improved since its introduction to the market (around 1980), present versions do not crack easily and meet the requirements of high ambient temperature operation of the battery.