https://www.techradar.com/news/iphone-xs-teardown-reveals-not-much-has-changed-inside-except-the-battery

If you’ve been wondering just how different the iPhone XS is from last year’s iPhone X, wonder no longer. Apple's fancy new smartphone and its bigger sibling, the iPhone XS Max, have been pried open by iFixit, and surprise, not much has changed – except for the new A12 chipset and a reshaped battery.

Yes, the pair of batteries in last year’s iPhone X have been merged into a peculiar L-shaped single unit in the iPhone XS, which is fitting given Apple’s tradition of designing its own custom batteries to fill the most internal space possible. Curiously, the new model’s battery is 2,659 mAh capacity, compared to the iPhone X battery’s 2,716 mAh.