Battery health issue

You are clearly using a 3rd party app to see battery count. And those programs are notoriously unreliable.

The fact is Battery Health declines normally. You can't stop it. It will continue to decline. And a decline in Battery Health of from 1-2% per month of ownership is normal and expected.

You suggest 52 months is likely a typo. I suspect you meant in 5 months, right? If that is correct, a drop in battery of 3% in 5 months is actually quite good and not something you should be worried about.

Since Apple started providing a Battery Health reading, it has caused people to worry needlessly over something which ALL batteries do. And this is lose the ability to hold the same level of charge from new over multiple battery charges.

It's highly unlikely that in 5 months of owning your iPhone it has only been through 36 battery recharge cycles. Especially if you charge your iPhone daily, like just about every person does. A battery cycle is from 0-100% charge. You likely don't drain your iPhone battery to 100% daily. If however, you use 50% charge in a day and charge it back to 100% that equals 1/2 battery cycle. It doesn't make much math to recognize that you've likely had more than 36 full cycle charges on your iPhone in 5 months.

Stop using 3rd party apps, which don't work well. Stop worrying about Battery Health decline, which you can't stop, even if you tried. Don't let your iPhone battery go below 20% charge. Charge it as often and as long as you want (you simply cannot overcharge an iPhone battery). Make sure you have Optimized Charging turned on and charge your phone every night while you sleep.

Read this article too --> Batteries - Maximizing Performance - Apple

Final note. If battery health is a major concern, you could switch to Samsung. Samsung doesn't let you see the actual battery health of their batteries. Only Apple provides that and that is to let you know that when your battery health dips in the future to 80% or less, it will then be time to invest in a battery replacement. You are a LONG TIME from there.

Some iPhone batteries out of the box have a bit higher capacity than the minimum capacity. Some have the minimum capacity. Trying to compare three phones of the same model is pointless. I'm willing to bet good money, the three of you don't use your phones the exact same amount of time each day, nor stream the same amount of content, nor spend the same amount of time on phone calls, reading emails, texting, etc.

It is pointless to try to compare three phones unless they are being used in a lab setting doing the exact same things at the exact same time.