It's premature optimization if you're caring about this in your prototype. It's not at all premature optimization to look at battery life before you ship.
The design decisions you make early on will stay with you. How you treat "occasionally connected" users is likely to have some architectural impact. Keep their requirements in mind as you sketch out your application.
I can understand what dllthomas is talking about. I'd never write a full-blown prototype, but whenever I'm writing a non-trivial app for myself it can be quite productive to write 10% of the app, throw that away, and start again. This strategy always gives me a better understanding of the problem, the app's architecture and so on, as well as a ton of new ideas.
Right, that's pretty much what I was talking about. Not so much something "officially blessed as a prototype" but "does this make sense at all?" experimentation shy of an MVP. I've heard "write it, throw it away, rewrite it" attributed to Knuth, and while that's overstating it a little you definitely learn things in your first attempt.
> The management question, therefore, is not whether to build a pilot system and throw it away. You will do that. […] Hence plan to throw one away; you will, anyhow.
