I have an Android on my IPv6 network with no issues, and this is across several different router vendors with different defaults for RAs. Maybe it's not an IPv6 issue and you're barking up the wrong tree?
Probably definitely barking up the wrong tree, yes. I happened upon a forum post somewhere about Sony Xperia XA2 battery drain on networks where router advertisment intervals were every 10 seconds or something.
Who knows, maybe I dreamed it.
Nonetheless, I disabled IPv6 again and that, somehow, was the smoking gun that solved the "my phone always runs out of charge overnight when I stay connected to your wi-fi" problem.
