I rarely put my linux to sleep because I had this experience in the past, but yesterday I've had my minisforum v3 laptop in sleep for 3 hours and it stayed fully charged at 100% battery. It made me think the battery percentage readout was broken, but no, it strarted draining after using it for a while.
No clue if it's something I did back then during install (arch linux btw) or whether it was like this out of the box, but it really surprised me. And I'm gonna try using it more in the future.