You're right. My battery life isn''t bad but Signal is the biggest drain on it. I'm also optimizing and restricting everything as much as possible.
Quoting this for other #GrapheneOS users, if you have battery drain then it's probably because you have Signal.
https://github.com/signalapp/Signal-Android/issues/13704
The hardened signal fork Molly is far more optimized and doesn't have this issue. A pull request was made to Signal to fix but they never merged it. Been ignored.
Discussion
I don't have the signal app and I find the Pixel 9 lasting days, and I use the battery limit feature.