Regarding battery life, I'd be curious to know how a modern smart phone would fare if you used it as infrequently as a dumbphone. When truly idle my nexus 5 seems to drain very little; it's the fact that it's so useful (and in turn so frequently used) that seems to be the issue here.
I understand why you say this, but I think this is not exactly the issue. I do carry an internet-capable device, whenever I might need one (i.e. less often than you would think).
If I were to carry a smartphone for this purpose then I would get a worse experience than I do on a larger screen, and it would hinder my ability to use telephony services when I need them.
For my needs, those services do not belong in one device.
For what it's worth, if battery life is important, my Note 3--about as far as you can get from a dumbphone--has amazing battery life. The battery meter barely goes down after an entire day. I occasionally don't charge it for two days and it's still green and going strong. It's literally never died on me. And I don't do anything particularly to keep the battery life up, like reducing screen brightness.
> Good, but other tests say it dies after 9 hours of browsing.
I wouldn't really know, because never have I been in a situation where I actually used my phone nonstop for 9 hours. =]
For my typical usage, the battery will last several days at least and probably a bit more if I put more effort into reducing battery consumption. I actually don't know how long it'll last since it's never died. Definitely not two weeks, but long enough for me to not really worry about the battery life.
All that said, I can definitely see the appeal of a phone that lasts two weeks. I think the Note 3 sits at a decent compromise between that and my old phone, a Galaxy S3, which could barely last 8 hours (of typical, very intermittent usage).
Battery life trumps navigation, for me, comfortably. If I'm lost after a long day, I need the option to phone my destination.