iPhone 8 only has a battery capacity of 1821 mAh, while the iPhone 7 has a battery with a capacity of 1960 mAh. In variants with bigger screen, iPhone 8 Plus has a battery capacity of 2675 mAh while iPhone 7 Plus 2.900 mAh.
Apple said the iPhone 8 should last as long as the iPhone 7, which is its predecessor. This may happen because Apple can usually perform battery optimization through software. It seems that software optimization is the reason why the iPhone 8 battery is smaller but Apple claims it can last as long as the iPhone 7.
Even so this news may make some Apple fans disappointed, especially because battery life is one of the important things considered when someone wants to buy a mobile phone.
The fact that Apple's competitors, like Google and Samsung, dare to offer batteries with greater capacity also does not help.
For comparison only, Pixel and Pixel XL which Google launched last year has a battery of 2,770 mAh and 3,450 mAh. While Samsung Galaxy S8 and S8 Plus have battery capacity of 3,000 mAh and 3,500 mAh.
Even so, Apple devices can usually last as long as the device.