With the launch of note9, the most "hot" upgrade was the increase in battery capacity, from 3300 to 4000, which is in the same exact shell as the note8, with a headphone jack and even an s-pen inside.
Every review coming out so far says that the phone easily lasts a full day with heavy use also, which is a good thing. Granted there are phones with even higher battery capacities but they are not in the higher end of the spectrum, i.e. they fall short of certain things, larger batteries coming to flagships is a first. (Yeah the p20 pro also included)
What this means is future Samsung phones certainly having larger batteries, and the new iphone (plus model) also slated to be big on battery life, other OEMs are bound to follow (except Google, as always, where the pixel3xl is reportedly going to get a 3430mAh one even in a mammoth 6.7 inch display).
While this article also shines some light into supercapacitors like the one in the note9's s-pen, and its ability to charge superfast, but also its negatives like not being able to put large amount of them in such a small form factor, it still merits atleast the use in a phone, which gives us hope of enhancements in technologies like these in the future.
Battery tech is one which hasnt really caught on, and its refreshing to see some progress in that direction.