Not plugging it in does not mean the battery is not used, it just means that the battery is always charged by the gasoline engine in the car, rather than from the electric grid
Plus. It will be even worse for the battery as it will always be close to zero (at least in vw group 1.4 phev)
I own one and like it though. But I charge daily (from solar when the weather allows so) and it is sufficient for my commutes so th engine only starts in long trips.
That makes sense! I'd still assume thats way less then ideal on fuel usage. Again anecdotal but my gramps is charging his on a regular wall plug. Takes long but gets the job done. And if not you still get to drive anyway, you're never stuck.