Battery tester

A dual color LED displays how flat a 12V battery is. A dual color LED is a single LED, that has three pins and with a red and green internal LED. If the batter is above 11.6V the LED shines green, if the battery is between 10.5V and 11.6V both the red and green LED of the dual LED shine, giving the dual LED an orange appearance and if the battery is below 10.5V the LED shines red.

Battery tester
Battery tester

Components

BC547 npn transistor
x1 dual color LED
x2 470 ohm resistors
x2 1k ohm resistors
x1 11V diode
x1 8V2 diode