Rapid battery health decline in iPhone 14 within a week

The phone is 7 months old. The battery should be at about 93% at this time. You really should send flowers to Apple for your remarkably good luck.

Your battery was actually at 102-103% when new, but this would have been displayed as 100%

I've seen drops of 3-4% in a month and then no drops for the next 3-4 months. Nothing to be concerned about. That battery is a chemical device. Decline will not be linear.

At 12 months, your battery should be at about 88-90%. At 24, it will be about time to replace the battery.

Don't try to babysit the battery. It is going to do what it is going to do. You will drive yourself crazy if you are checking the battery all the time.

Use Optimized Battery Charging and connect the charger to the phone at night and leave it connected all night.....every night.

Drops in Battery health are not linear so you cannot guess what future drops will be from what you have seen over the last 10 days. Your battery is expected to last for 500 charge cycles where the Battery Health would drop below 80% and need replaced. The amount of time that takes depends on each user.

My recommendation for charging is to use Optimized Charging and charge your phone all night, every night. More damage will be done to your phone if you let it run out of power, so you never want that to happen.

Other than that, enjoy your phone. It is doing much better than average as usually you will see about a 1% drop per month. Again that is an average and the drop will not be linear meaning some months will not drop at all and others will drop more.