While the iPhone XS uses an L-shaped logic board, the leaked iPhone XI board has a rectangular shape. It's possible that Apple may have redesigned the board in order to accommodate a larger battery.
In April, analyst Ming-Chi Kuo predicted that the battery of the 6.5-inch iPhone could increase by 10-15% while the battery of the 5.8-inch iPhone could grow by 20-25%. The 6.1-inch iPhone XR successor isn't expected to get more than a 0-5% increase in battery capacity.
Alongside the larger battery, Apple's next generation iPhones are said to offer bilateral charging capabilities, letting them charge another iPhone or any other Qi-based device (ie AirPods).
You can check out the purported logic board images below and follow iClarified on Twitter, Facebook, Google+, or RSS for further updates. Apple will likely unveil its next generation iPhones this fall.