Being far from a cell tower would also place a lot of stress on the battery, so hiking by itself is probably more draining than you'd expect

TheDong, can you test if putting it on air plane mode makes any difference? Maybe you're on the edge of multiple cell towers and your phone is trying to connect/disconnect too aggresively?

Yeah, of course airplane mode makes my phone last longer, but what's the point of a phone in airplane mode?

It lasts longer if I turn it off too.

At this point I just accept that I have to bring a battery brick with me everywhere, it's fine.