The processor chips in newer phones use less power than older chips. This more-or-less compensates for the increased functionality. I'd say the effective battery life of the Samsung flagship phones has stayed roughly the same over the years, despite small variations from model to model. In any case, I always take a small external power pack, just to be sure.
I'm currently using a Galaxy Note 3, but it is gradually losing functionality (the headphone socket has failed, the portrait/landscape rotation sensor has failed, and a few other niggles). I'm definitely only considering a waterproof phone for its replacement.
I will consider the Note 8 when it is released next month. It's my understanding that, even in the rain, you can use it effectively with the stylus. I have tried a few waterproof phones in the rain and, while the waterproofing may protect the innards of the phone from the rain, it's hard to interact with the phone because the screen also responds to the raindrops that your finger is swirling around. However, the stylus is detected differently and may not have this problem. That's the theory anyway.
If I don't get the Note 8, I will consider the LG G6, because I strongly prefer its flat screen to the curved screen of the Samsung flagships. I find it a bit fiddly to hold a curved screen device tightly while navigating in the bush, without accidentally touching the screen near its edges.
Mapping and navigation is the main use of my phone. I'm evaluating phones according to the following criteria:
- Screen brightness, for map-reading in the bright Australian sunshine
- Screen size, to reduce the amount of scrolling and zooming that is needed (but it still needs to fit in my pocket)
- Loudspeaker volume, e.g. for when the phone is in my pocket and I'm near a noisy waterfall
- Waterproofness (not just "shower-proofness")
- Fast processor, for rendering vector maps on-the-fly
- Plenty of memory, so that I can keep vector maps for all my walking areas permanently on the phone
One thing I am NOT concerned about is screen resolution. I don't anticipate using the phone for virtual reality applications. For bushwalking applications, I don't think there is any benefit from resolution greater than the 1920 by 1080 that my current phone has.