When Apple acknowledged that they were indeed slowing down older iPhones with degrading batteries, alongside the discounted battery replacements, Apple also announced that they will be introducing a new feature in iOS that would provide users with more transparency regarding the health of their batteries.
The good news is that it looks like that feature could be part of the iOS 11.3 update. In the latest beta of the update, the new feature dubbed “Battery Health” was spotted. Basically this is an info page that lets users know the state of their battery, such as its maximum capacity (over time li-on batteries start to lose their max capacity).
It also tells them if their batteries are degraded to the point where they are experiencing unexpected shutdowns, which depending on the state of the battery, users can then choose to throttle their phone’s performance. It is unclear as to how degraded a battery must be before it affects the performance of a handset as a battery whose capacity is at 95% doesn’t get that option, while a battery at 79% is given that option.
That being said, it should be pointed out that the feature is currently in beta which means that Apple could make changes to it ahead of its public release, so what you see now might not necessarily be the final product.