General tips apply primarily: turn off wifi and bluetooth adaptors, unmount and disconnect any external drives and media cards where possible, turn screen brightness down, close any other apps that may be running in the background, and if you haven't already, install tlp which automatically changes settings in the background to optimise battery life. I believe performance is better with the NVidia proprietary driver but I don't know if that carries to battery life. My guess is that it would since it may be making better use of hardware acceleration. You may be able to tweak Nvidia settings for optimising battery life. Experiment.
You will also probably get much better life using mpv video player too. You may want to use a GUI though to make it easier to use though I'm quite happy with the command line and its minimal GUI. See what works best for you. The advantage of the command line mpv is the logs. You'll have to try out a few different drivers to see what works for you (I would guess VDPAU would give the best performance). Using mpv with the verbose switch (mpv -v) gives helpful information with regards to your driver's capabilities. Let us know what configuration works well for you.
NB As an aside, mpv is the only Linux player I've found that handles colour management. When configured properly, deliveres by far the most superior quality.