Battery Tester/Indicator/Monitor

This is a battery tester circuit.This circuit is used to indicate whether the level of a battery voltage is  normal, under-voltage, or over-voltage, very useful to make sure an electrical system will works properly. This circuit displays three classes of voltage level condition: high, low and normal. This circuit defines high level voltage if the voltage is more than 15 V,  low  is under 11 V,  and  normal is between 11 and 15 V. If the voltage is normal, the LED will be off. The LED will light constantly if the voltage is low and blinks at a 1Hz rate when the voltage is high. Here is the schematic diagram of the circuit: