This is an exaggerated take. I've been running Signal on LineageOS for years across at least 5 different phones in exactly this manner with no Google services installed. I'm currently using a Motorola G84 and charge every 2 days with moderate usage; Signal is my primary communication method with family.

The G84 has a very good battery by default though, judging from its predecessor. It can take some additional strain. Something weaker will suffer more.