Why is my iPhone 15 Pro battery dropping fast after only 6 months?

You are expected to get 1000 charge cycles before your battery needs to be replaced when it reaches 80%. The drop you see will not be linear and a 2% drop over a couple of days means nothing. That does not mean that in the next couple of days it will drop 2 more percent. With your cycle count, you should be showing about 90% Maximum Capacity, so you can see for yourself how that compares to the average. Once you get to 750 charge cycles, you should be about 85%, so of course it is expected to decrease.

As for seeing what is consuming your battery power. It is best to post the screenshot by going to Settings > Battery, and scroll towards the bottom. You will want to include the graph for the last 24 hours and the Battery Usage by App. Some apps include Background Processes that will continue to use your battery even if you are not using the app. This has nothing to do with the Background App Refresh setting you referred to.

If you have any Meta apps, those have specifically been noted as being power hogs. You will see many articles about the behavior of their apps on the internet and also the same posts reported over on the Google Support site for the Android users. Once you have identified a power hungry app, try deleting it and compare your results. If your battery performance has returned to normal, you now know the cause of the problem and the choice will be yours if you want to continue to use that app or not.

Battery Health decline is NOT linear, meaning it can remain steady for a while then drop a couple of points all at once. One would expect an iPhone with 500 charge cycles to have a Battery Health in the range of 90%. For about every 50 cycles a corresponding 1% decline is normal. You suggest your health declined a couple points in a couple days. That isn't unusual. You didn't say what the current Battery Health is?

You simply cannot stop battery health decline. Batteries are consumable parts and with every full cycle charge your battery health will decline. It's normal. When the health of your battery dips to 80%, which it WILL do if you own your phone long enough, it will then be time to pay Apple to replace the battery.

Again, what is the current Battery Health on your phone?

nhor9999 wrote:

My current battery health now is 90%. I'm just wondering, will my battery health reduce very fast the same next time?

Or is it because of iOS 18.5? I just want to figure out if the battery of the iPhone is broken on something. I just need to know the cause of this problem.

Your battery health is exactly where it should be after 500 charge cycles. Your phone isn't broken and two of us have explained there is NO problem. Did you actually read what me and Mac Jim ID posted about your battery?