@bpr thanks for reporting back on what you are seeing. I’m remembering now that there are a few pull requests that needed to be merged for Stop mode to work and session move to also work. These won’t be present in v0.4.8-rc.6 or v0.4.9, but will be in the next Electron firmware release so keep an eye out for that (coming soon).
SoC will update very slowly over time, so any immediate changes to the battery state won’t be noticed. You can call .quickStart(); to rebase the SoC value but there is currently no automated way to do this (detecting that you are running on USB power only). I’m not sure there will ever be a system event type of way to detect this (removal of the battery) either since an open battery looks very much like a high resistance battery (charges up instantly). I won’t go into ways you could do this in your application code right now, but I think it should be possible if that’s something you need.