A friends at use the battery often meet a problem electric its energy is finished in important always may many good if there is the circuit warns before or there is the way checks at the beginning. By this circuit use the transistor just one and don’t have to have power supply source. By this circuit designs to come to use battery 3V – 15V. By fining decorates with VR1. When level voltage agree more location dot keeps LED1 as a result bright immediately. This circuit uses electronic part the a little , then easy in building , request friends , enjoy please yes.