Why did my iPhone 15 Pro Max's battery health drop from 99% to 98% after only 10 charging cycles?

First of all your Battery Health didn't decline after only 2 charging cycles. Your Battery Health declined after 114 cycles. Battery Health decline is not linear, meaning it can remain steady for a while, then drop a couple points. On average, you will see about a 1% decline in battery health for every 25 to 50 cycles, so your battery is doing exactly as it should and there is nothing to be concerned about.

Your Battery Health is perfect, so nothing to worry about there. The battery graph indicates a 50% drop in capacity over 12 hours which is also expected even with 2 and half hours or reported screen time. The phone is still doing background processes even with Background App Refresh turned off and will perform iCloud backups, index files, perform object detection on photos along with the many other system processes.

While I see no indication of a "stuck" system process consuming power, if that was the case I would recommend doing a Force Restart:

• Press and quickly release volume up
• Press and quickly release volume down
• Press and hold side button until the Apple Logo appears. Ignore anything else on the screen while holding the button and it could take up to 15 seconds before you see the Apple Logo.

Your iPhone is expected to drop 1% battery health per 50 charge cycles. After your 114 charge cycles, you roughly should be at around 98%, as displayed. Note that your iPhone’s battery decline is not linear and while it seems that it dropped after 10 charge cycles, your entire battery health is normal and on-track.

The question is how long was your Battery Health at 99%? Apple rounds down. So in reality, your capacity was at 99.0 and now it’s at 98.0 and you’re worried about a 1/10 of a point drop. Short term drops are irrelevant. Apple measures battery health in 100’s of charge cycles and you’re trying to micromanage your battery health. You can do it.

You can micro-manage the battery all you want, but what you can't do is stop Battery Health decline. Batteries are consumable parts and with every full cycle charge, they lose some battery health. Since three of us have told you there is nothing wrong, you can continue to worry over what you can't change, or just enjoy your phone as it is performing exactly as expected.

Jobayer_Islam wrote:

I have Turned of Background app refresh,Location Service,Reduced White point,Reduced Notifications,Turned off auto brightness,Tuned off talk to siri,No homepod,No car-play…Then why its not Giving at least 5 hrs of Screen on Time?

I am just using Mobile Data,Spotify,and some basic Calls and messages in my Socials.

I don't see why it would show 5 hours of Screen Time. Turning off Background App Refresh does not stop Background Processes from running and those will continue to use your battery even when your screen is off.