Mine always made it through a full day with room to spare. I guess it depends on how much you use it. I said charge every night to be safe, but I think I actually only charge mine twice a trip. I only take a few movies a day though and maybe 50 pictures tops.
With the ZS7, the battery went down faster due to the GPS, but I just got back from New Orleans and only charged it once while there. Took a couple of movies and about 200 pictures.
Sounds about similiar, we don't take a ton of pics and only a movie here and there. It looks like I'm going to go with the ZS7 because it is so close in price to the ZS3. I'm not sure I will ever need the GPS but for the little bit extra money I figure its worth going w/ the newer model.