Battery Draining too fast after ios 15.4.1 and new batteries in two Phones

We have two iphoneX models that were working fine with different settings and battery conditions at 81% and 80%. After the ios 15.4.1 updates they both started to experience extreme battery draining and heating . We took both phones into an Apple store Where they ran diagnostics and replaced both batteries at our expense. That night they both went from 100% to 15 and 17% while idle. This is crazy as the phones have become useless and the Apple tech did not see anything wrong with the phones. We have removed half the apps. turned OFF ALL notifications. Gone to Fetch for mail. Only using wifi, Turned off location settings and all background updates. We have made them Dumb phones with new batteries. In other words .... they have become useless. This has to be a result to the last Update but if any one has any ideas that we may have missed it sure would be appreciated as the Apple techs that we talked to did not have any ideas. The only concrete suggestion they had was to move the screen lock from 3 minutes to 30 seconds. It didnt make any difference but it did make sense.....