I am using JB omega rom v. 56 with Boeffla kernel 5.1. When I am home and connected to wifi 'Android System' drains the battery extremely quick. It goes from 100% to 70% in one hour. And that's when I am not even unlocking it to check the time.
When I'm outside and not connected to wifi there's like 1% battery drain an hour.
There is an option where the phone will disable wifi when the phone is locked. It's worth a shot. FYI, if there is any background downloading or something when the phone is locked, it may use up mobile data, so be careful if you try that.
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