To get over 12 hours of battery life out of a 60 Wh battery - which isn't impressive nowadays with laptops rocking 20+ hours - you need to stay below 5 watts of battery draw on average, and considering that the machine will likely do some actual computation occasionally, you'll need to idle closer to 2-3 watts at the battery including the monitor and any conversion losses.
The really big gains in battery life are from cutting tens to hundreds of mW off things at the bottom by keeping hardware off and using fixed function hardware like e.g. avoiding rendering and doing direct scanout and using partial panel self refresh. Execution units do not turn on and off instantly so pinging them even briefly is bad, and the entire system needs to be aligned with the goal of only using them when necessary for them to stay off.
Efforts like libliftoff to do efficient plane offload to avoid render steps in the display server can save in the area of half a watt or more, but it's not a whole lot of help if applications don't do their part.
Bigger GPUs than your iGPU (or even just later iGPUs) will also likely see even bigger impacts, as their bigger shader units are likely much hungrier.
(As an aside, I am not a fan of kitty - they have really weird frame management and terrible recommendations on their wiki. Foot, alacritty or if ghostty turns out good, maybe even that would be better suggestions. Note that comparing to foot can give a wrong image, as CPU-based rendering pushes work to the display server and gives the illusion of being faster and more efficient than it really is.)