Originally Posted By: mlord
The really funny thing, is that the phones are SLOW even when on AC power.

And it also affects some (all?) laptops as well, again on AC power, even with the old battery unplugged.

Weird.

The take-away I got from it is that, if one has a an Apple product that is feeling more sluggish than before, REPLACE THE BATTERY before thinking about an upgrade to the latest shiny toy!

Or at least follow the lead from that article and check the CPU clock speeds using the free (and almost free) tools linked in the article. This is a really easy issue to verify, regardless of the web site used to publicize it. wink

Pure speculation on my part ...

Perhaps the underclocking (when an old battery is in use) is in part to reduce thermal stress on the aged battery. Especially in a mobile device, the heat generating components are not far from the battery mass. If heat adversely affects an old battery and increases degradation risk or accelerates aging rates then underclocking may be helpful for squeezing some residual longevity from a battery that is already declining.

I seem to recall a modern iPhone will reduce clock rates as the device internally warms beyond some level. I have had sun exposure overheat an iPhone enough that it switches to a survival mode, only showing a warning message regarding temperature.

There is enormous variation in how different individuals use their iPhones, and use the batteries. I often encounter people who regularly run the iPhone battery down to near zero before recharge. Some cannot be bothered to charge it more frequently, others think it is ‘healthy’ to deep cycle the battery level often.

Even when all iPhone batteries meet a high quality bar from the factory, variations in device usage will induce battery longevity and stamina variability.

The drive for ever improving device functionality in very compact form factors inevitably puts a stress on battery lifespan and capacity.

My understanding is that the external battery case made by Apple for the non-Plus size iPhone provides intelligent battery management of both the external and internal batteries. I suspect the overall calendar lifespan of the internal battery is substantially extended when the battery case is in use.

I will admit I am in the camp of preferring a couple more mm in iPhone design thickness to provide more battery capacity. I always use a shell case on my iPhone, another mm or 2 would not be a problem. For me. I can see that many people value device thinness, and certainly thin devices (not just from Apple) sell in huge numbers.