“Are they going to increase the battery size to account for the power used to transmit sound to headphones?”
No. It’s a typical crappy Apple thing - no more typical headphone/microphone port - instead it’s Apple’s proprietary lightning connector - so everyone will have to pay a royalty to Apple for converters.
Another reason why I don’t have Apple products.
One of my sons has the Samsung 5 and another has the I phone.
Once my oldest saw the Samsung and how hecan download movies and music for free he now wants the Samsung as it is much better.