One way around this, if you want work/life balance, is to timeslice on much longer increments, like a couple of years instead of a couple of days. Put in the long hours at the demanding job for a few years until you have a shippable product and demonstrable, tangible successes. Then take a year off to travel, found a startup, work on an open-source project, volunteer, or otherwise decompress, using the savings you got from the high-paying job before.
For some reason, taking a year off to travel, volunteer, or experience the world isn't looked at in the same negative career light that wanting to only work part-time is, particularly if you have demonstrable successes at your last employer. It shows passion, engagement, and the ability to take responsibility for your own life, and many employers assume that will transfer over to your job performance at your next job. You're at a slight disadvantage in salary negotiations because they don't have to lure you away from your existing job, but you can make up for this by applying to many jobs (ideally through connections) at once.
I've heard it's also better on the "life" side of things as well, as you can throw your whole being into whatever you experience in your free time, and not just settle for the scraps you can fit around your job.