well, i see a problem with this circuit.
first, the leds D11-D20 don't have there cathodes connected to anything. they come connected to the GND, like the rest of the leds.
secondly, the leds will not fade out when you turn off the power, because there is no cap that holds the energy they require to keep illuminating after power is cut off.
maybe someone has a solution for this ? considering that there are 20 leds, quite a large cp is required.
how about having the circuit connected to the power suply, and have some sort of an ON control, so like when the ON is connected to the +12V then the circuit will think that it is on. so it will fade in the leds. then when the ON is disconected from the +12V then the circuit will think it is turned of, and it wil fade out, but the energy it needs to fade out is not from a very large cap, but it is still drawn from the battery.
sounds good?