Battery discharge status indication circuit 5

The right side of the dotted line in the figure is the simplest series-connected transistor regulated power supply. Connect the anode of the voltage regulator tube
vs to the base of the indicator transistor VTz, which can be used to monitor the battery voltage.
    When the battery is discharged to a voltage of Uz+0.7V (where U; is the voltage stabilization value of the voltage regulator tube vs), the transistor VT2 is cut off, VTi is turned on, and the light-emitting diode VL lights up, indicating that the battery
needs to be charged or replaced. .