Valve regulated lead-acid (VRLA) batteries named SEH65 series for hybrid vehicles have long been used in hybrid inverter-controlled motor and retarder system (HIMR) buses developed by Hino Motors Ltd. In order to elucidate the points for improving the battery performance, the battery performance, which were obtained during field use and by bench test, was analyzed in details. As the result, a new VRLA battery, with which longer life performance can be expected, has been developed by improving the positive grid corrosion resistance and adopting a new additive for the negative plates. In addition, it was found that estimation of residual life of the battery is possible by measuring the battery voltage in high-rate discharging during bus use and by adjusting it with the field use conditions. (C) 2003 Elsevier B.V. All rights reserved.