During yesterday's presentation Apple, as usual, nothing was announced about the battery capacity of the new iPhones. However, the video demonstrating the new technology 3D Touch in the frame is the battery capacity iPhone 6s.
The video confirms that the iPhone 6s comes with a 1715mAh battery that was previously assumed. This is almost 100mAh less than the battery iPhone 6 which has a capacity of 1810mAh.
Reports also indicated that the battery capacity of the iPhone 6s Plus will be reduced to 2750mAh, while the battery capacity of the iPhone 6 Plus will be 2910mAh. This information is not yet confirmed, but it is likely that a working prototype was presented in the video iPhone.
There may be several reasons why the newer iPhone will be less battery than the previous model, this may be due to the size of the Taptic Engine and the chip 3D Touch, which take up a significant portion of the motherboard. In any case, one can only hope that the difference of 100mAh will not greatly affect the battery performance of the iPhone 6s and iPhone 6s Plus.