battery health

See this excerpt from 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. 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. 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%.

From your numbers you seem to be pretty close to anticipated loss. Despite having used close to a third (157) of the 500 charges you have only lost a quarter (5% out of the permissible 80%) battery health one might expect.

The bottom line is, if just before the end of a year you are at or below 80% then have it inspected by Apple to determine if it is a warrant-able replacement.

Jos05 wrote: "...Can someone tell me why, after just several charging cycles, my phone's battery health deteriorates by 1%?"

Jos ~ Because that % is only an algorithmic estimate of a dynamic chemical process.

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