An uninterruptible power supply with an input terminal and an output terminal, a main switch connected to the input terminal, an input filter circuit connected to the main switch, a rectifier circuit connected to the input filter circuit, a main capacitor connected to the rectifier circuit, a switching device connected to the capacitor and the output terminal, a voltage boost circuit connected to the capacitor and a battery input terminal, a slope control circuit connected to the voltage boost circuit, a slope selection circuit connected to the slope control circuit, and a control board connected to the slope selection circuit, where the control board has a central processing unit and memory.