In order to know the working state of UPS in time, the terminal voltage of single battery (rated at 12V) should be measured every six months. If the voltage difference exceeds 1V, the balanced constant voltage current limiting charging should be used, otherwise the battery can only be replaced. If there is no power cut in the local area for a long time, the power supply must be interrupted manually on a regular basis to discharge the UPS with load, which can extend the life of the battery. It is impossible to know whether the battery is normal if the power has not been cut off for a long time. In fact, once the power has been cut off, it may provide a very short discharge time or even fail to discharge power at all, because the battery is in floating charge for a long time