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Performance isn't lowered to extend battery life, it's lowered because the degradation in old batteries makes it impossible to reliably run the processor at max

Performance isn't lowered to extend battery life, it's lowered because the degradation in old batteries makes it impossible to reliably run the processor at max clock; if you flip a switch to force high clocks despite an old battery, your phone will randomly shut down sometimes. So they couldn't really run the CPU full speed for years. They sure could have, say, highlighted to users that a battery replacement can make an old phone run better for longer, but of course they'd much rather users replace their phones. Or, as another comment here suggested, they could have left more margin--overspecced the battery so it could run the CPU at higher speeds even once it was somewhat degraded, rather than putting so much of the efficiency gain over iPhone generations into thinness and lightness. Might also help battery life for heavy users.

CamperBob2 9y ago
Performance isn't lowered to extend battery life, it's lowered because the degradation in old batteries makes it impossible to reliably run the processor at max clock; if you flip a switch to force high clocks despite an old battery, your phone will randomly shut down sometimes. That may be what they're telling people, but there is absolutely no engineering basis for it. Battery voltages decrease gradually under all normal operating conditions, and switched-mode converters can extract useful energy from them throughout the entire discharge regime. The main constraint on battery voltage isn't some mysterious "random shutdown" effect, but the health of the battery itself. If you allow the battery voltage to fall too low -- which will, again, happen gradually and not instantaneously -- its service life will be greatly impaired. This is not something that happens without warning. It's a perfectly well understood effect. Once the phone's CPU sees this happening, it will have plenty of time to post a "Shutting down in xx seconds" message to the user, go into emergency low-power mode, or otherwise take action to protect the battery.
- twotwotwo 9y ago
  Even those that skeptical of what Apple did here seem to think there's some real limit on safe power draw involved. If that can be shown false it could probably be a popular blog post here at least.

CamperBob2 9y ago

Performance isn't lowered to extend battery life, it's lowered because the degradation in old batteries makes it impossible to reliably run the processor at max clock; if you flip a switch to force high clocks despite an old battery, your phone will randomly shut down sometimes. That may be what they're telling people, but there is absolutely no engineering basis for it. Battery voltages decrease gradually under all normal operating conditions, and switched-mode converters can extract useful energy from them throughout the entire discharge regime. The main constraint on battery voltage isn't some mysterious "random shutdown" effect, but the health of the battery itself. If you allow the battery voltage to fall too low -- which will, again, happen gradually and not instantaneously -- its service life will be greatly impaired. This is not something that happens without warning. It's a perfectly well understood effect. Once the phone's CPU sees this happening, it will have plenty of time to post a "Shutting down in xx seconds" message to the user, go into emergency low-power mode, or otherwise take action to protect the battery.

twotwotwo 9y ago
Even those that skeptical of what Apple did here seem to think there's some real limit on safe power draw involved. If that can be shown false it could probably be a popular blog post here at least.