If the M1X 16" keeps the battery size of the current model, which is the largest possible battery you can take on an airplane, it will run a bit shorter than the M1 Air at full throttle (but get more done in that time), but significantly longer than the M1 Air for casual use, because it's presumably using the exact same efficiency cores.
Depends on what they do with GPU. If they put in desktop-class(-ish) graphics, then that would impact battery life heavily (and make me super happy OTOH).
MacBook Air M1: 49.9Wh | MacBook Pro 16" 2019: 100Wh
The 16" MacBook Pro is rumored to have double the performance CPU cores, and either double or 4x the GPU cores. So for tasks that are strictly GPU bound, battery life could be about half of the M1 Air.
Considering that this is the absolute worst case scenario battery life (assuming of course that they don't make the battery smaller), the new 16" Pro is looking pretty exciting.
Beefier graphics often improves battery life (more cores at lower clock, like nvidia mobile vs desktop for the same model number: lower TDP, same perf). They might move to more power hungry RAM as part of it though.
The on-chip GPU Apple ships in their MBPs draws way less power than the dedicated Nvidia chip. This is especially noticeable in the battery life drop that occurs when the dedicated chip is used exclusively.
On chip/package has many power advantages, and Apple is on a much newer process node with M1 (TSMC 5nm).
The point I was making was that e.g. a GTX 2070 desktop has around the same compute power as the mobile version, but the mobile version uses much less power. It does this by being beefier (2560 CUDA cores mobile 2070, 2304 CUDA cores desktop 2070), but running at a lower clock.
