Changes in the internal resistance and the voltage, together with the rusulting amount of discharge of an electrolyte-limiting motorcycle VRLA battery were examined in its excess discharging through a fixed resistor for an extended period of time. In such excess discharging, the internal resistance increased at the beginning to exceed 100Ω, but later decreased to become a few Ω. The rate of the increase of the internal resistance and its maximum value, as well as the rate of its subsequent decrease depended on the resistivity of the fixed resistor. On the other hand, the battery voltage gradually decreased during the excess discharging to reach approximately 11V (slightly lower than 2V/cell), during which the theoretical discharge capacity dictated by the amount of the electrolyte was completely exhausted. After that, the voltage dropped sharply to almost level off at approximately 5V (slightly lower than 1V/cell), followed by a subsequent sharp drop to reach OV. The discharge after the sulfuric acid had been consumed was considered to be caused by the reaction of the positive electrode active material with water to form PbO, which eventually covered the grid surface to cause an extremely high internal resistance. When the battery was kept standing after the voltage had reached OV, the electrolyte became alkaline due to hydrolysis reaction, which made the internal resistance substantially low.
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