If I have it fully charged, remove the cable, and then put it in suspend (or close the lid, which suspends) and leave it about 24 hours, the laptop will have suffered a power-loss and the battery be fully drained. While suspended, the laptop can also be noticeably warm.
I’m running KDE on Arch Linux. I read that the HDMI port had significant power draw for some reason, so I’ve ensured I don’t have it attached (currently I have two USB-C, one USB-A, and one Micro-SD port).
There’s a bug in upower, and possibly elsewhere, that is preventing proper suspend. The GUI buttons in KDE weren’t actually triggering suspend at all for me. Closing the lid as trigger is similarly unreliable in my experience. Not sure on the status of the fix.
I recommend you use hibernate from command line if you have that working (I do) or full shutdown (and make sure it finishes full shutdown until the power button light goes off before lid close) for now.
Based on the discussion in that thread, people are observing that their system is not entering a suspend mode successfully. However, if I execute journal-ctl | grep suspend I get logs that appear to show that the system is indeed suspending: