I used the P&C kit for a while with my 360 and I grew tired of having to use the cable to recharge the battery. I ended up using Eneloops and I could never go back to using a wire to charge the controller. It's just not practical for me having something that always gets in the way.
Having an internal battery in the DS3 was nice. Not needing to buy AA bateries and having great battery life is definitely a plus in my book. Having said that, we shouldn't pretend that irreplaceable internal batteries don't have any shortcomings.
To me, the XB1 controller fixes the major battery-related problems with the 360 controller:
- The bulge is gone. That makes the form factor a lot better, something that I honestly didn't believe was possible while still using AA bateries.
- There's no propietary power cable and the controller will work as a wired controller.
- Battery drain when not used is a lot better.
- You can use Li-ion packs now if you prefer those, and they will be user replaceable. I bet it won't be long until we see some cheap Chinese alternatives.
The only disadvantages I see to the XB1's controller battery design are, obviously, the need to pay for batteries and, probably, the added weight, although I'd have to get my hands on one before making up my mind about that. Apart from that, it's a really flexible approach and a definite improvement over the 360 controller. Personally, I still have plenty of Eneloops around and I like my wireless controllers wireless.