So, lookig at new hardware there is big spread in battery life between office work and gaming.
But I cant find battery life in older games so, has anyone experience in these cpus and resource hogs like Heroes of might nd magic 3, Sid meiers colonization, Alpha centauri - these kind of games?

I do not own the recent hardware in question, but, I am curious to know if you are aware of the CPU-usage fix for Alpha Centauri. While launching said game through 'loader.exe', regardless of hardware, system resource utilization is low. Prior to employing this work-around, while playing Alpha Centauri, usage of a single thread had stood at 100%.

In the past, I had read that it might be just as effective for other games of that era (including, but, not limited to: SimCity 4, as well as some of the Heroes of Might and Magic games).

It even functions as expected within Wine (though, if I am remembering correctly, it may have been necessary to compile the executable and DLL from source (rather than using those included within the release)):
export WINEPREFIX="$HOME/example/path"; cd "$WINEPREFIX/drive_c/Alpha_Centauri" || exit; exec wine loader.exe -e terran.exe

Dosbox is very much a light touch compared to using a VM or such things. Especially if you use a modern port such as Staging, which continues to drag the codebase kicking and screaming into the modern age; now featuring multithreaded audio slated for next release.

SMAC you might be able to wrangle into shape with Gamescope + frame limiting; I can't imagine it needs much more than 60. glsmac is far from ready, but perhaps one day.