Battery life has been a bit inconsistent. Usually I get around 4 or 5 hours screen on time, though honestly my habit with all my phone Shas been to charge them whenever possible. If I'm driving, I set it on the mount and plug it in. If I'm at home or work and not using it, I plug it in (or in this case set it on the wireless charger). But I was fairly unimpressed with the S8+ battery life.
Yesterday and today, I turned on the medium battery power setting. It seems to have increased my screen on time dramatically, but I'm also at home and on wifi.
Medium decreases screen brightness by 10%, sets resolution to FHD+, underclocks by 30%, and turns off the AOD. Of these, the only thing I miss is the AOD, but it also seems to make the most difference in battery life.
Either way, my battery life today is much better. So far I've had almost five and a half hours of screen on time and 54% battery remaining. That's all surfing the internet, posting here, texting my wife, taking a few photos, and a little Facebook. I'd say that is fairly impressive.
I'll see how the battery holds out Monday when I'm away from wifi, driving through varying cell tower coverage areas. I'll also check how it is if I turn the AOD back on. I do like the AOD.