This is the simplest type of Voltage Monitor you can build in 5 minutes. No need for a PCB and just solder lead to lead and hook up in the Emergency lamp. As long as the battery voltage is above 5 volts, LED lights to indicate a healthy battery. When the battery voltage drops below 4.7 volts, LED turns off to indicate the time for charging. It is a must for emergency lamp since deep discharge permanently destroys the battery. Let us see what is happening in the emergency lamp battery.
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