Why don't you just carry a battery pack? https://www.samsung.com/us/mobile/mo...b-pg950csegus/
That battery is light and small enough to be used at the same time while charging your phone. The battery fits in my pocket along with my note 8. I get over 10% charge in 10mins. that's about one hour gain in runtime.
All the highend phone uses more or less the same chip the difference is the larger battery. You don't have many options if you want battery capacity larger than 3000Mah. Reviewers don't test the power saving but you can gain maybe an hour if you turn on CPU limiter.
Massdrop sells the Mate 10 for $699 at checkout.
Samsung s9+ will be available next month. I think with its new chip you'll see a small gain in battery runtime.