First off wqhd+ doesn’t take any more battery than fhd+, all the pixels, the same exact pixels making up your screen are still physically turned on and use the same amount of power.

Only difference could come in from ui rendering, but as all the ui is 2d, again you aren’t using any more gpu processing power so no power savings from there either.

Only in 3d games will there be a slight difference, for games that actually render at 1440p and in 3d.

If you want to feel placebo you could use the phone on lower res you can but you will not see any actual battery difference.