The so-called "iPhone 8" will adopt a higher-cost stacked logic board design to support longer battery life, according to KGI Securities analyst Ming-Chi Kuo.

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.

Kuo said the stacked logic board, also known as a "substrate-like PCB mainboard," will result in the "iPhone 8" with an OLED display having similar dimensions to a 4.7-inch iPhone, yet comparable battery life to a 5.5-inch iPhone. He expects the device to have around a 2,700 mAh L-shaped two-cell battery pack.

Kuo added that the battery life of "iPhone 8" with an OLED display could be better than that of a 5.5" model with a traditional LCD display, as OLED panels are more energy-efficient than their LCD counterparts. For comparison, the iPhone 7 has a 1,960 mAh battery and the iPhone 7 Plus has a 2,900 mAh battery.