The iPhone has a built-in lithium-ion polymer battery. This type of battery deteriorates with repeated use and eventually reaches the end of its useful life, but the "day" differs depending on the frequency of charge and discharge and how it is used.
In the first place, when it comes to battery life, the meaning changes depending on whether it works barely, but it has dropped significantly from the original performance, or it does not work at all.
Apple's official view (LinkIn ), the battery life is the service life, which is "the duration until the battery needs to be replaced with a new battery", but the specific number is not shown. However, because the AppleCare+ warranty covers "when the storage capacity of the battery has deteriorated to less than 80% of the original", it can be said that it is a general idea to set the life as the time when it falls below this "80%". Would be
In other words, it is only necessary to check the current (full-charged) charge ratio to the original charge capacity, which is very easy. Open the screen in the order of "Settings" → "Battery" → "Battery status" and check the value of the "Maximum capacity" item. If it is 80% or more, there is no problem, and if it is 80% or less, it means that it is in a state of being used even though it has reached the end of its life (while enduring performance degradation).
Even if you don't check this screen, sudden shutdowns often occur (probably due to low battery voltage), and the back is swollen (due to expansion due to deterioration of the battery pack). , You can determine that the battery life has expired. If this happens, you will not be able to use it while suffering from performance degradation, so let's make a reservation at the Apple Store and replace the battery.