To maintain your battery health at 85% and beyond, update your iPhone regularly. Here’s how: Go to Settings > General > Software Update. Tap Download and Install if an update is available. Connect your iPhone to a power source and Wi-Fi network. Let the update install, and follow the on-screen instructions. Tip 5: Monitor Your Battery HealthNow, of course you'll use it with less than 25% battery occasionally or in emergencies. Also, this 20% threshold behaves proportionally, meaning using you iPhone with 1-5% is WAY WORSE than using it with 15-20%. But yes; bad consequences generally start at 20%. Hope many people find this helpful! took me a while, and it's proved cause-effect You will start to see CPU throttling or random shutdown below that point. At 90% - 100% is good battery health for used iPhone. anything near 80% will require replacement. Depends what iPhone are you looking to buy depends on the cost and if you want to repair it yourself.
However, this can help change the battery heath maximum capacity to its actual value, so I recommend this to people as it won't diminish iPhone battery lifespan. I have heard op's complaining about their battery health maximum capacity reading is dropping from 100 to 85 in a few months and this is not normal, hence a calibration may solve this
Is Battery Health in iPhone real ? My battery life reduced to 85% more than 1.3 years ago. It's still haven't changed. My device gets heats up sometime and with irregular charging pattern and with Optimised for Battery function turned off still I couldn't top it off. Device: iPhone XReCFFi.