Generally a 12V battery is expected to produce a 12V dc voltage all the time until it gets discharged. Practically, it is not possible and the output voltage of the battery decreases gradually as load connected to it draws current from it. So it is generally considered that if the output voltage of a 12V battery changes from 12V to 9V approximately, it is constant and after the voltage falls below 9V, it is considered to be discharged and need to be charged again. Any inverter designed to use with a 12V battery should be comfortable to produce a constant AC output voltage during the fall of battery voltage from 12V to 9v approximately. My point to say all these is that to monitor a 12V battery, it is sufficient to monitor the battery voltage from 12V to 9V range and a voltage below 9V should give a warning for LOW BATTERY VOLTAGE. Here for the development of the circuit, the 12V to 9V range is divided into 6 parts as 9V, 9.5V, 10V…11.5V. So 6 op amps are used to compare and display the appropriate level of voltage. The circuit is simple. Comparison is done between the two terminals of each op amp and accordingly output is shown. The series of resistors connected at the inverting terminals of each op amp makes a voltage divider and exact comparing voltage is supplied to each op amp.