I don’t think it’s simply a matter of not liking to carry spare batteries around. The reason I prefer rechargables has to do with predictability. When I had 312s, somehow the battery low message - the 15minute warning - would often come at a really inopportune time. Like playing in a band concert and being on stage just about to perform, or just after your doctor calls you to discuss your medical situation. With most rechargables, other than Lumity, as long as I charge them overnight, they’re good for whatever the next day throws at me.
I’ve trialed a few; right now I’m wearing Resound Nexia. I’m usually up at least 18 hours a day, stream 2-3 hours, and when I pop them in the charger they usually have about 60% battery left. On a very bad travel day, I wore them for 21 hours. By the way, I had also trialed the Resound Omnia, and their hours on an overnight charge was pretty bad. Resound has made a big improvement with the Nexia.