My Iphone 15 Pro Battery Health Dropped Faster than 12 Pro

Cycles are the number of times you have charged from 0% to 100%, or any combination that adds up to 100% (such as 50% to 100% twice, of 75% to 100% 4 times). It is merely a count, and an accurate one.

On average, your capacity will lose about 1% for every 25 full charge cycles. So after 118 cycles it should be at 95%. As yours is at 97% it is doing better than average. Thus, the rate at which your 15 Pro is dropping is unusual, because it is BETTER THAN SHOULD BE EXPECTED.

A battery is a chemical device, and chemistry is generally pretty variable and uncertain, as well as being analog, not digital. Apple specs the battery capacity to remain above 80% for 500 full charge cycles, but that is a minimum requirement; there is no published maximum expected capacity. So sometimes batteries will perform much better than that minimum specification, and sometimes the change in maximum capacity won't be linear. There is no way to predict in advance what the real-life performance of any specific battery will be.

All iPhones have a specification for the battery. As an example, for the iPhone 14 Pro that is 3200 milliampere-hours (MaH). So the battery monitor is calibrated for 100% at that value. But there are variations in manufacturing, so some batteries will have less capacity, and some will have more. Suppose your battery had, say, 3520 MaH capacity (10% over standard). That would still show as 100% (even though it was actually 110%), but as it aged the health would stay at 100% until it fell below 3200 MaH. This would appear to you as if the battery had fabulous life, until suddenly it didn’t. It appears that your older phones had batteries that far exceeded the minimum specifications, so you were lucky. Even your 15 exceeds the minimum specifications.

On average, Battery Health will decline about 1% for every 25 charge cycles, or in normal use about 1% per month. So your battery dropping by 3% over 118 charge cycles is normal and actually a bit better than average. The degradation in battery health is not linear nor precisely predictable, so you may see sudden drops, increases is some cases, or things remaining stable for a time. Even experienced battery engineers cannot predict with any accuracy how any given battery will degrade over time.

So there's nothing wrong with your iPhone 15. What it's showing is not at all unusual. Your iPhone 12 was much, much better that usual. Mine over the same period dropped to 84% battery health.

Regards.