A small simple circuit with available components to measure the voltage level of any battery by its voltage Percentage by set adjusted potentiometer R2 to set the first green LED as you want highest volte or full batter,and red led wite low volte.

  And you can set the rate of decrease or increase voltage between each LED by potentiometer R1; for example:

The circuit can be set in the range of 12.7 to 10.7

Or set Between 12.7 to 12 or set 10 to 9 volts Or 13 to 9 volts….ect

It supports wide range of voltage from from 4 volt to 24 volt batteries

The circuit includes protection from Reverse polarity that happen with some users when connecte incorrectly