The 'substrate-like PCB mainboard' will allow let Apple fit nearly a 5.5-inch iPhone sized battery pack into a device with comparable dimensions to the 4.7-inch iPhone. Kuo believes the iPhone 8 will have a 2700 mAh L-shaped two-cell battery pack.
As battery material tech isn’t likely to see major breakthroughs in the next 3-5 years, mainboard area can only be reduced via stacked SLP, which makes space for larger battery and extended usage time. Thanks to stacked SLP, we expect the OLED iPhone to have similar dimensions to a 4.7” TFT-LCD iPhone, and have comparable battery capacity (equipped with around 2,700 mAh L-shaped 2-cell battery pack) to a 5.5” TFT-LCD iPhone. The battery life of the OLED iPhone could be better than that of the 5.5” TFT-LCD model as OLED panels are more energy-efficient than their TFT-LCD counterparts.
Since OLED displays are more energy efficient than LCD, the iPhone 8 could have better battery life than the 5.5-inch LCD iPhone. Currently the iPhone 7 has a 1960 mAh battery and the larger iPhone 7 Plus has a 2900 mAh battery. Apple is said to be primarily using OLED display panels from Samsung.
The iPhone 8 or 'iPhone X' will likely launch in September of this year. Please follow iClarified on Twitter, Facebook, Google+, or RSS for updates.