As you can see in the chart above, some older (gray) phones like Pixel 2 or iPhone 8 also have buffalo batteries than new ones (blue) like Pixel 3 or iPhone XS.
There are many factors that affect the phone's battery life, but the main factor is probably the screen. New technologies such as OLED will consume more power, or so will the use of high-resolution screens and maximum brightness.
iPhone XR and Galaxy Note 9 are two phones that beat all others. iPhone XR uses LCD screen with low resolution, while Samsung for Note 9 battery is bigger than its predecessor (4.000mAH while Note 8 uses only 3,300mAH battery).
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