ZedEffective noted that what battery engineers view to be a healthy battery is different than what your average, everyday consumer thinks is normal. When a lithium-ion battery’s capacity falls to around 70%-80%, that’s actually considered the battery’s end of life (EOL). [Source 1, 2]
These batteries work by moving lithium ions between graphite and another material. Over time the materials age and become damaged. During this process, it’s normal for side effects to occur. The main causes of “cell death” include:
- Repeated cycling damages and cracks the graphite anode, lowering the amount of ions able to be intercalated into it
- Lithium metal plates on the anode and can pose thermal risk, also lowers total Li-ions available for cycling
- Passivation layers increase cell resistance past a practically useable point, and the cell cannot draw peak current
The last effect is the biggest reason why your iPhone shuts down when it has 50% battery left. Batteries are active chemical systems and can only perform at peak capacity for a limited number of times before they start to degrade.
From this perspective, Apple’s throttling of the battery is an attempt to minimize the number of these side effects and shutdowns. So to a battery scientist, this is perfectly reasonable.
Of course, Apple should have communicated this better to consumers. Simplicity is the raison d‘être of the iPhone, but maybe the class action lawsuits could have been avoided if the company used clear language to explain what could happen before it happened.
It’s also interesting to note that the iPhone is Apple’s last product operating on a 500 cycle battery. Other devices, like the Apple Watch, iPads, and MacBooks have batteries meant to last at least 1000 cycles.
Backup & Restore
Finally, as Michael Glenn notes, if your iPhone is acting up, try performing a full backup and restore. You can back up your iPhone using iCloud, iTunes, or a third-party app like iMazing. Then, go to Settings > General > Reset > Erase All Content and Settings on your iPhone. This should only be used as a last resort, but if the newest iOS 11 updates haven’t fixed bugs you may have, then it’s worthwhile to try something else before you bring it to an Apple store.