The battery can be left on for the entire season, all day and night, and you will never run out of juice. As a matter of fact you can leave it on for an entire year, in the gun cabinet, and get it out the following Spring, and it will still have battery power left...........don't ask me how I know.
FF3 has an auto shut off after 12-14 hours. But yes, it would last for about a year with the same battery if it could stay on..