If you want to power the Roam off completely, you need to press and hold the power button for about 5 seconds until you hear a descending chime sound. Or enable Battery Saver in the Sonos app so the Roam will automatically power off after about 30 minutes of being idle.

Maybe one or two per-cent a week when it’s ‘fully’ powered off, or thereabouts? However there’s much more battery drain if the Roam is left in sleep mode (battery saver not enabled) and I understand higher external temperatures can affect the level too.