If you set up hibernate, then it will not drain the battery at all, as hibernate is completely powered off (contents of RAM are written to disk and reloaded on startup).

I agree with you on suspend, though: even with "deep" sleep enabled ("s2idle" is garbage), I still lose about 20% overnight.

I find my macbook (M1, Air) achieves really good battery life when I'm actively using it as my main computer (so including sleep/hibernate) but extremely poor when I'm not. For example if I turn my Macbook completely off and leave it for a month, the batteries drained completely.

I've had the similar experiences with a 2017 Macbook Air at my previous job. Over time it got worse to the point it'd be at 100% when it suspends at the end of the day and then when I was back at work the next morning there was a 50:50 chance it'd be completely flat. I eventually had to get into the habit of plugging in my Macbook in the morning for ~5mins before starting it up to ensure it didn't try and start on 0% battery and promptly shutdown. The same machine would last all day (i.e. charged to 100% first thing in the morning and then disconnected from power and used on battery the rest of the day) which seems to rule out battery capacity issues. YMMV.

> I can throw my macbook into a bag and pull out a week later with just a small battery draw down

Hmm, I can't with a Macbook Air M1. I lose maybe up to 10% a day.

When suspended, I see it appearing on the network a few times each hour. I can leave a process running in the background and see that it's getting a few seconds of cpu time each time this "suspended" mac wakes up to do whatever it is doing. There are no settings I can see for a deeper sleep and to stop it doing whatever it is doing. I think they check for updates and such.

My KDE Slimbook with openSUSE does a great job. Comfortably lasts a whole workday, and the standby works fine, too.