When I visited the South Island last year and rented a (gasoline) car I was struck by how little infrastructure there was even in the towns. And on the freeways there was almost nothing by the side of the road between towns every 30-50 miles.
All in all, north island driving distances are just pretty small. And the roads so windy you need a rest before you’d run out of juice.
Drastically different to Australia where you can drive at 110km/h in a dead straight line for hours on end.