Android 9 will have 4.4 Kernel. AEX already uses it. Still a bit bugged, but very promising.
But in terms of battery life in my opinion still MIUI 9 is the best and even MIUI 10 is better than AEX or RR ROMs , especially standby times. In MiUI ROMs I guess there is very aggressive background data control which makes standby battery life very good. But as a minus notification problems happen constantly in MIUI ROMs
I wish there would be a ROM with standby times like MIUI, performance like RR and supports latest Gcam with OIS.. I guess I'm asking too much ))
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