iPhone X and Samsung Galaxy S9 are the top of the range of the moment and undergo several comparative tests. The last, related to the battery capacity, have shown that the S9 is less than Android competitors but also to Apple.
The Galaxy S9 has an average duration of 7 hours and 23 minutes of use, lower than the 8 hours and 22 minutes of the Galaxy S8. iPhone X reaches 8 hours and 41 minutes while the average Android competition is around 9 hours.
Apparently, the problem depends on two factors: first the new Exynos 9810 processor that is more performing than the one mounted on the S8 but with higher consumption. Secondly, Samsung did not want to overdo it either at the software level with the optimization algorithms of consumption nor hardware with more capacious batteries to avoid repeating the disaster that occurred with Note 7.
According to the tests, Apple has achieved a good optimization on the battery between software and processor as both offer maximum performance requiring minimum effort and minimum consumption.