DrAzzy:
You should also use a better battery. A stack of 4 AA's (for 6v) into Vin/Raw would do it (it might not give you quite 5v, but for this application it should be fine. USB doesn't give you 5v on pro mini or nano either)
Ok i'll test with the 4 AA's but yo think i can put a 6V on arduino nano without causing any problem to the circuit, and i ask you if you don't know a better way to power the circuit with battery, that can stay for 3 or 4 month.