My Phone Battery is not lasting more than 8 hrs !!!

I have an Iphone 8 that was put into service in October. Its less than seven months old and my battery percentage is 88% . It has been going down for 7-8 weeks. My phone is still under warranty but through Apple and ATT secondary insurance. After getting no help via Apple support I sent a strongly worded email to senior management. It got a response. I worked with a high level support tech to try and troubleshoot the problem. He had me do all the steps that are circulating including a number of diagnostic downloads from my phone . The outcome was less than satisfying, in fact it was shocking. It basically amounted to too bad, nothing we can do there might be a software update in the future!!! That’s Apple’s position!!!

They say its software , I say they have lots of bad batteries and they know it and are stalling till they get sued AGAIN !!!