METHOD FOR DETECTING WHETHER A BATTERY IS DISCONNECTED, AN ONLINE UNINTERRUPTIBLE POWER SYSTEM AND AN OFFLINE UNINTERRUPTIBLE POWER SYSTEM USING THE METHOD

A method for detecting whether a battery is disconnected, an online UPS and an offline UPS using the method. The method comprises the following steps: determining whether a charging circuit charging a battery is in a constant voltage charging mode; and when the determination result is yes, executing a battery disconnection detection, which comprising the following steps: alternately performing a first operation and a second operation on a PWM signal, wherein the duty cycle of the PWM signal is used to control the output voltage of the charging circuit, the first operation is increasing the duty cycle of the PWM signal by a first preset value for a first preset time, and the second operation is reverting the PWM signal to the original duty cycle for a second preset time; and determining whether the voltage at the output terminal of the charging circuit rises and reaches a second preset value.