I believe my iPhone 15 Pro Max Battery is defective

As a long-time iPhone user, I take pride in maintaining my devices in the best possible condition. My past devices, the iPhone 13 Pro Max and 14 Pro Max, managed to retain their battery health at 100% for at least 11 ½ months of daily use. I also practice the habit of charging them only to 80% and still manage to get a full day of use.

However, ever since I upgraded to the iPhone 15 Pro Max, I have been facing battery performance issues, mainly related to how quickly the battery drains during normal daily use. In just 30 minutes of using WhatsApp and Facebook, I can observe a drop of 8-10% in battery life. The phone no longer lasts as long as my previous two models did. For instance, I can go to sleep with an 80% battery (in airplane mode) and wake up to find it at 75%. As soon as I check my device for 10-15 minutes, another 3-5% disappears. The rate at which the battery drops is deeply concerning and unacceptable.

My biggest concern happened today. After only one month of use and at 25 charge cycles, my battery health dropped from 100% to 99%. While I understand that, based on Apple's standards, this is considered normal as batteries are expected to degrade 20% after 500 charge cycles, I'm sharing my perspective considering the following:

1. My iPhone 13/14 Pro Max devices maintained 100% battery health for over 11 months.
2. Two of my friends using the same device model still have 100% battery health even after 26 and 30 charge cycles.

You might wonder why I'm so concerned. Well, I need my device to retain as much battery health as possible because I sell my device annually to upgrade to the latest model. If the battery health falls below 90%, the selling price is significantly lower (at least $200-$300 lower some shops might not even accept the device).

As a Pro model user, I'm genuinely upset by this. Spending this much on a device shouldn't result in worse performance than my previous device. Is it possible that I received a device from the initial batch with a defective battery, or am I just one of the unlucky few? I wish Apple could provide an answer or, at the very least, replace my defective battery for free.