For optimal battery life you need to tweak the whole OS stack for the hardware. You need to make sure all the peripherals are set up right to go into the right idle states without causing user-visible latency on wake-up. (Note that often just one peripheral being out of tune here can mess up the whole system's power performance. Also the correct settings here depend on your software stack). You need to make sure that cpufreq and cpuidle governors work nicely with the particular foibles of your platform's CPUs. Ditto for the task scheduler. Then, ditto for a bunch of random userspace code (audio + rendering pipeline for example). The list goes on and on. This work gets done in Android and ChromeOS.