@scalz said in Serial gateway running on coin cells. Needs to sleep: also forget bad coincell brands, not good at all for lifetime. This is my biggest concern at the moment. With the watch device I can resort to Lipo and recharge if needed, but the sender is best encased in silicone to protect it so its crucial that I get a long reliable battery life from it. My only option there is to use inductive charging. Which might be easy but I've not looked at the details. I would also need to do shipping safety sheets if I use lipo but I think that it's probably just an expense. Not a project risk.