How do you make leds show the percentage or charge of a capacitor

I wonder how make leds show the level the charge of capacitor im developing a coil gun/magnetic accelerator and i need too know when the capacitors are charged

How do you know when the capacitor is charged?

I would make the led blink faster depending on the amount of charge.

CF the blink without delay example.

Use one of the Analog to Digital converters to read the voltage across the capacitor or use a resistor divider if the voltage is too high. You could have 5 leds and at full charge all five will light, at 80% 4 leds will light, etc...

Is this what you were thinking?