The following sequence is useful to show the battery voltage (battery) 12 volts. Voltage level is shown with four lights led. To facilitate the reading of the led is arranged in a vertical array. Led top three chosen by the green LED while the lowest is selected the color red. If the battery voltage continues to decline (because of usage), the Led-Led will turn off sequentially from the top to the bottom.
Until if battery voltage is below 11.83 volts then only the red LED that lights up which means that the charge batteries are empty. Even this red Led will die if the stress continues to drop to below 11.5 volts. The working principle of this circuit is a comparison of battery voltage with a reference voltage.
Schematic Battery level indicator