The Nikon D810 battery life is exceptional and never a reason to complain.
The Nikon D850 appears to carry that forward and better it with greater power efficiency and the Nikon EN-EL15a.
Shoot for extended periods without worry — Long battery life
The D850 allows you to concentrate on shooting without having to worry about battery life. The camera can shoot up to approx. 1840 still images*1 from a single charge of an EN-EL15a/EN-EL15 Rechargeable Li-ion Battery, thanks to its energy-efficient power circuit and EXPEED 5 imageprocessing engine.
An optional weather- and dust-resistant MB-D18 Multi-Power Battery Pack can also be used as a power source, enabling shooting of up to 5140 images
Take that Sony! Sony cameras are too small for my hands, and the batteries have to be small because of it—not a great idea IMO. Still, I do get a few hundred exposures off a Sony battery, so I just carry some extras and usually 3 is enough for a full day.
As a bonus, batteries from the Nikon D810 and other Nikon DSLR models (Nikon EN-EL15) is compatible so I do not have to go out and buy an all new set of batteries.
Why Nikon publishes blurry hardly readable screen shots in the brochure, I dunno.