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Here is a Simple LED Volt meter to Monitor the charge level in Lead Acid Battery or Tubular battery. The terminal voltage of the battery is indicated through a four stage LED indicators. The nominal terminal voltage of a Lead Acid battery is thirteen.8 volts and that of a Tubular battery is 14.8 volts when totally costd. The LED voltmeter uses four Zener diodes to light the LEDs at the exact breakdown voltage of the Zener diodes. Usually the Zener diode requires 1.6 volts in excess than its prescribed worth to be triumphant in the breakdown threshold degree. When the battery clings 13.6 volts or more, all the Zener breakdown and all LEDs illuminate. When the battery is discharged below 10.6 volts, the entire LEDs stay darkish. So depending on the terminal voltage of the battery, LEDs remove darkness from one after the other or flips off.