You need the play/charge kit to charge while playing, or to be able to 'dock' your controller. You can't charge standard rechargeables inside the controller AFAIK.
Interesting. I never had a problem with keeping AA's charged for various devices around the house, so I never really looked seriously at a play and charge kit type setup.
But my curiosity now has me looking around a bit. Looks like there is an obvious market hole for an all in one solution, and while there may be some fundamental EE reason why it isn't a good idea, I'm not seeing it.
So the energizer stand for $30 comes with the battery packs, so for equivalent price to DS4 + stand you get the choice of charging on a stand like DS4 or swapping standard rechargeables as many of us do (an option I don't ever want to lose due to the aforementioned kids). But you can't charge while you play via cable, if that's your thing.
The nyko kit for $13 has two battery packs and USB charging cables, so for that additional cost you can charge like stock DS4 or swap standard AA's.
Or, get both, and for the <$20 premium over PS4 + stand, choose whichever of the three methods works for the current situation.
But why are these functions segregated? Why not a replacement pack that instead of having what looks like two encased AA cells, just allows you to insert any AA NiMH cells, will charge them by USB, will charge them on a stand, and will allow you to swap out the cells for fresh ones if desired?
Since I have never physically examined any of these up close, I have to assume its a size problem. Maybe the NiMH cells in the plug and play and stand charged versions are smaller than two standard AA cells, to make room for.charging circuitry? Can't be that big of a difference if so. And if that's the case, I wonder if the physical sizes make that impossible or just difficult. And if impossible, I wonder how big an impact dropping to two AAA cells would make?