Recharging one's batteries entails doing something that feeds oneself. Basic stuff like getting enough exercise and rest and eating good food can't be neglected without getting burnt out, but there are other things to consider, too.
Anyone who isn't an utter recluse and qualifies as a responsible adult usually has a number of obligations. Some are real, and some are imagined. Obligations entail giving something to someone else. There has to be something to give, however, and that is difficult to do when one's batteries are drained.
So one has to balance one's obligations to others against the need to care for oneself. Recharging one's batteries includes doing stuff which one takes pleasure in because it pleases oneself — if it happens to directly gratify others, too, that is all well and good, but the emphasis should be on doing it because it feeds oneself. It might be as simple as spending quiet time in a hammock, it might be learning a new skill, it might be considerably more complicated.