When the battery is full of electricity, it will cause negative capacity to be higher than positive capacity when it continues charging. The gas produced by the positive electrode is combined with the cadmium produced by the negative electrode. In general, the internal pressure of the battery will not increase obviously, but if the charging current is too large or the charging time is too long, the oxygen produced is too late to be consumed, which may cause the rise of the internal pressure, the deformation of the battery, the leakage of liquid and so on. At the same time, its electrical performance will also be significantly reduced.