Does battery calibration affect battery health percentage reading?

No, and there is no reason to calibrate any iPhone newer than the iPhone 4. And note that you are not calibrating the battery, you are calibrating the battery gauge. It doesn’t change the condition of the battery, just how accurate the battery gauge will be.

Andropple wrote:

Hi Laurence, u r right. the battery calibration is about the gauge and not the battery. But the percentage of the battery health must come somewhere. Only thing I can imagine so far is the battery health algorithm is using data from the battery gauge (charging and discharging load/times and battery charge percentage) to estimate the percentage battery health. If the gauge reference is changed after a calibration. Does this affect also the battery health percentage?

No, nothing affects battery health percentage. Batteries are consumables; they lose a little capacity every time they are discharged, then recharged. On average this works out to about a 1% loss for every 25 “full charge cycles”. As one example, if you charge the phone overnight, every night (and that is what you should do; it is a best practice), it starts the day at 100%. If it drops to 20% by the end of the day before you charge it again overnight that counts as 0.8 full charge cycles (20% to 100%), or about 24 full charge cycles per month of use. For this example your battery capacity will lose about 1% per month. Of course, if the end-of-day level is higher than 20% the capacity loss will be a little less, and if it is lower than 20%, or you charge it during the day, the capacity loss will be higher.

The absolute best way to get maximum use on a charge, as well as slow the decline of battery capacity long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern. If you enable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates.

It’s constantly evaluating the condition of the battery. The traditional method of running a battery down until auto shutoff is known as Coulomb counting, where the power management determines how much energy is used to determine the capacity of the battery. It matters somewhat since it’s used to determine how to run, when to do certain things, etc. The state of the battery is stored on nonvolatile memory in the onboard logic.

But yeah the battery health could be updated if there’s something that happens that shows that the previous battery health is incorrect or otherwise needs to be updated. Battery health is just an estimate based on behavioral models. I’ve even heard of cases where reported battery health went up 1-2%. It doesn’t mean that actual capacity increased.

Lawrence Finch wrote:

No, nothing affects battery health percentage. Batteries are consumables; they lose a little capacity every time they are discharged, then recharged.

It is just an estimate though based on all sorts of models and observations. If the estimation is off it's possible that it just shuts down before it reaches 0%. I just saw that happen on my MacBook Pro (which has needed a battery replacement for some time) and the reported "Full Charge Capacity" dropped more than 10% as reported in System Information and by coconutBattery. However, Macs have been known for having that reported capacity go down rapidly only to have it go up. I've had a case where I suspected that the system went sideways and corrupted the data - reporting negative battery capacity.