The nominal voltage of the battery is +12V, and the reference voltage for A/D conversion is +5V, so two resistors R48 and R47 are used to divide the battery voltage and then sent to the MCU’s AN2 for A/D conversion. R48 is 3K. R47 is 1K, so the voltage sent to the A/D conversion is 1/4 of the battery voltage, which meets the requirements of the A/D conversion for the input voltage. When the system is in an idle state, the battery voltage is lower than 11V; when the system is in an inflated state, the battery voltage is lower than 10V; when the system is in an emergency start state and the battery voltage is lower than 7.8V, the system will give a low voltage alarm. LCD displays "BatterylowRechargesoon" and flashes, and the buzzer sounds an alarm.　　 When the user wants to charge the battery, he only needs to plug the +15V regulated power supply into the charging socket of the system. The positive end of the external regulated voltage is divided by R44 and R45 and sent to RA4 of the MCU. When the MCU detects that RA4 changes from low to high, it starts to charge the battery. The charging adopts PWM1 control of MCU, the battery is less than 13.5V as a stage, and greater than 13.5V is a stage, when the battery is greater than or equal to 14V, stop charging the battery.