Question: why pixel 4 has small battery?
Answer: Google put a little too much faith in its ability to use software optimizations to improve efficiency; that or the hardware team doesn't fully understand the power requirements for the phone. And even if you look at “fit-in-hand,” the Pixel 4 is 8.2mm thin; the iPhone 11 Pro is 8.1mm, and has a 3,046mAh cell.