The huge touch-display lies beneath the battery.

The logic board is beneath the metal shield at the top of the image (under the 2D barcode).

The Touch battery is 54.0 x 64.1 x 2.8 mm, while the iPhone battery is 43.6 x 50.5 x 5.4 mm. That puts the volume of the Touch battery (9588 mm^3) at 81% that of the iPhone (11780 mm^3).