It would be a radical departure from what Apple has typically been good at, which is to take technology and software that already exists, design a great product in that segment (although it should be a segment that is currently small but poised for big growth), typically make sure that product has better software, usability, etc than what already exists, and then sell it as a revolutionary product that is the first of its kind with a massive media blitz. Make sure all of your branding and marketing sell the idea that absolutely nothing like this has ever existed before.
They already outsource their manufacturing but the battery market is huge. I don’t think they can grab the Powerwall idea from Tesla and market it as a new thing. And if there is one exec that I would expect to push back hard against Apple with those shenanigans it’s Musk.