Under normal conditions, the mains power is charged through an adjustable rechargeable battery, while the self starting relay battery+24V voltage is sampled through voltage sharing. The sampling voltage Vo is applied to the V1 base through R2 and VD3, causing 1 to be in a linear amplification state and deeply saturated. The DC control relay K sucks 4V voltage and sends it to the V+terminal of the inverter through K and K1. When the inverter relay is powered off, the input voltage+24V remains unchanged when K1 is cut off. After K continues to pull on K2's self-locking action and still sends it to the inverter room normally, the battery voltage begins to decrease in a downward direction, The conduction of VI 1 weakens and V2 increases; When the voltage of the battery rises to a certain value (i.e. the battery voltage drops to 22V), V saturation enters linear amplification, and V3 quickly feedbacks back to the base of ^ 1, causing V2 to form a rapid cutoff. K is disconnected, and the+24V DC sent by the battery to the inverter is cut off. The inverter stops using the battery for power, and the book battery quickly recovers to 24 samples of saturation. At this time, both K1 and K2 are disconnected from the inverter, and the inverter protects the book battery. After the mains power returns to normal, K1 is closed, and the inverter can charge the battery at this time.