Iphone XR battery drop 1% in just 2 days

Referring to the "Your battery's maximum capacity" section of the support article: iPhone Battery and Performance - Apple Support

"A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions." Even rechargeable batteries get worn down and 1-2% health loss per month is perfectly normal. According to iPhone Battery and Performance - Apple Support , Apple apparently only considers it unusual (and warrant-able) if a battery drops below 80% maximum capacity in less than a year after you receive it. Ergo, some storage loss as you use it is anticipated and acceptable. Prorating that possible 20% drop over the first 12 months equates to 1-2% drop per month being within the range of what Apple finds acceptable. "The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge." In other words, if maximum capacity is below 80%, the battery is below normal performance and worth replacing. You can still use a device with a lower health percentage than 80% but for optimal usage you may wish to consider having it changed when it reaches 80% battery health.

- If battery health drops a few percentage per month that is normal.

- If battery health drops below 80% in the first year, contact Apple about a warranty replacement. (Apple will test it to determine its actual eligibility.)

- If battery health drops below 80% after the first year, consider getting the battery replaced but anticipate paying for it.

99.9% will display as 99%.

Lawrence Fitch will likely expound on this.

Why are you not connecting the phone to the power adapter at night and leaving it connected all night.....every night?

This is the single most important thing that you can do to maintain the Battery Health on your phone.

The Battery Health percentage numbers are confusing many users because the of the unusual way that Apple has designed the software to "round" the numbers.

For example, the battery might be at 100.0% and drop only 0.1% to 99.9%, but due to rounding, the Battery Health display number will read 99%.......not the true number of 99.9%.

Over a number of months, the battery will drop an average of about 1% a month. Some months, it will not drop at all and other months it might drop 2%. All of this is normal.

Expect to replace the battery in about 2 years.

For example, the battery might be at 100.0% and drop only 0.1% to 99.9%, but due to rounding, the Battery Health display number will read 99%.......not the true number of 99.9%.

I presume Apple follows standard conventions with rounding and 99.9% would round to 100%. It's only when it drops from 99.5% to 99.4% that it drops to 99%.

Likely what he will say is given the possible inaccuracies of the battery health calculation based on a modeling of chemical processes, that a 1% drop is nothing. The device likely comes out of hte factory at 100% the day it come out but the second a battery is produced it starts ageing so it may well have been at 99.99% before it was even in the box.

Unless Apple has its own way of doing things, all science researchers and financial people in the world use standard rounding conventions.