even after updating apps instantly after a security patch or os update your devices may lag or drain battery.. Basically there is no problem.. After every software update the cache memory is disturbed (tip:clear cache after every update in recovery mode, it will help a lot for major problems).
And Every smartphone today comes with many silent A.I. features which keep detecting your useage patterns for couple of days, this may drain a little more battery initially.
But after a week of update phone starts working normally as before.
Some bugs might cause battery to drain but they are resolved in next update. Don't worry.