That's true about some apps. Don't know why I didn't think of that. Most of the ones you'd use in a grocery store don't require service at all. Some of the apps say you don't need to be connected, but some don't.
As for a battery.. mine is new obviously and my iPhone is 1.5 yrs. My daughter has had apple products for quite a while and she's never mentioned replacing batteries. I think that most batteries last a long time and if they do need replacing some of them are not replaceable in apple products. Never been an issue with anyone I know.