iOS 11.3 Beta 2 finally adds the iPhone battery health sub-menu2
To redeem itself for this lack of communication, Apple lowered the price for replacing an iPhone battery down to $29 and promised that a future update will let the users know what their batteries' health currently is and also allow them to disable the throttling manually. Now, with iOS 11.3 Beta 2, we finally get a glimpse of this new menu!
To get to it, you go to Settings → Battery where you will find a brand-new menu, called Battery Health (Beta). Opening that up will give you a reading for your battery's Maximum Capacity. Basically, if this number falls below 80% — it's time to consider a replacement.
If your iPhone suffers from another unexpected restart, the power throttling will activate again.
So, you will need to go back in the same menu to turn it off again, if you so wish.
If the battery's health is degraded to a point it needs replacement, this page will also suggest a link, which will lead you to the nearest Apple-certified repair centers.