15.4.1 in battery drain issue
Battery drain issue in 15.4.1 fastly to 15.3
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Hey there ,
It is assumed that an update has solved the battery drain problem. If you are still facing this problem, you should Contact Apple for support and service - Apple Support
But before you do that go to Settings > Battery > battery using by app , Check out the applications that consume the battery heavily. If there is nothing that consumes the battery heavily, there may be a technical problem Or if you replace the battery by a store that is not approved by Apple, it may be non-native and may cause the battery to drain and if your battery health is 80% or less you need to replace it!
and also see this article’s might help you: