https://news.ycombinator.com/item?id=25101115 One of the dev behind plasma mobile commented on that a few days ago.
If you just let it sleep (modem on registered to the network, allowing for voice calls, all the rest of the phone suspended), you'll get about 24 hours of runtime.
I think there's still more power management fixes that can be done, mostly in BT/Wifi, but it's not bad at all for a phone that's still tagged as "dev"