Re: Apple admits it slows down older phones
Get an app called "Battery Life". It will show you the battery wear level. If you keep your device topped off (wireless charging makes this even easier), the battery will stay in good shape for years or essentially past the useful life of the device. Don't leave it in a car in extreme heat or cold, etc.
If your battery is excessively worn, its peak current output is going to be severely hampered. When a device demands higher peaks, battery voltages can sag low enough to respring the device. The newer builds take battery condition into play and will adjust CPU throttle curves in accordance to prevent random resprings. This will definitely have an impact on performance overall. Its similar to using a battery saver profile on a laptop.
Users with slower devices have reported that changing batteries in those devices did restore performance so there's that.
The only change, IMO, there should be is a pop up notification that would basically tell you that the battery is worn and performance is degraded. Replacing the battery would restore performance.
The idea behind this is, simply, a slow device is better than a device that randomly shuts off or restarts. Apple should just notify the users why.