The wcw backpacks don't turn themselves off, they keep going till you switch it off. Is it the yellow colured one you got ?
I use mine all day as I don't have a van system. It does me 10 houses a day. I tend to put it on charge before I go to bed, though there has been a few occasions I've forgot and its done me the whole next day too. Don't know if it would run for a third day though.