Your power grid — aka, your overall
life bar for each campaign — will not
regenerate at the end of each battle.
The good thing about Fantasy
Life is that, since everything you do raises
bars, there's little downside to not completing things in your own world; guarding your miner friend isn't just charity, as you're raising your combat skill, and there's no worry about raiding friends» worlds of resources, since everything
regenerates fairly quickly and can be collected again later.