I think it is more of the first scenarios. I think the once the Battery hits a certain % it will kick on to keep the battery from draining completely to Zero. But they haven't really said. Its just what I've noticed watching videos from CES. I hope they give us some more info so we can all stop speculating....so does '150 miles' BEV range mean that's when RE will switch itself on by default? Reducing rate of discharge of the smaller battery and extending to '500 miles'?
Or does that mean that's when the smaller battery for EREV is exhausted w/ RE disabled, and you then need to park to plug-in and/or recharge via generator? So perhaps RE defaults to switch on around 75 or 100 miles?