Mike (and others), the 7805 output is (only) 4.79V, with input at 12.55V (see picture) (Pb battery), I assume the low voltage is due to high current/power drain (0.23A = not far 2W), I don't think the low voltage could be the origin of the high consumption (the Atmega328 is given for 1.8-5.5V, downgrading clock with low voltage, but 4.79V is normal to +-5%)
I've also found Atmega328 temp is climbing very Hot (not as the 7805 but too hot for this kind of circuit), that might be the original problem, is it a defective nano board ? (despite this it start to work fine)
73 - Remi
