Step 1: 11 Volts
Step 2: 12 Volts
Step 3: 13 Volts
Step 4: 14 Volts
I have built a simply and little part of this beautiful circuit, You can add extra steps whatever you want, you can also change the voltage of the Zender Diode.
In the real life you can easily changes the green leds with RGB ones, and set the circuit like this: Low level of Battery --> Red Led; Medium level of Battery -->Yellow Led; High level of Battery --> Green Led.
