Why your iPhone battery meter sometimes goes haywire

The problem is that these bizarre battery issues extend back to the still-in-use iPhone 5S and through to the iPhone 6S. They include battery percentage free falls, where you can watch your battery life drain from, say, 30% to zero in the space of a few minutes or suddenly shut down with 20-30% battery life remaining.


Pretty much, anyone, I mentioned iPhone battery issues knew what I was talking about or had the experience to share.

Apple won't comment on what's going on with the iPhone's rechargeable lithium-ion batteries or the iOS software that manages them, and it hasn't acknowledged any issue beyond unexpected shutdowns on some iPhones.

Late last year Apple did reveal that a small number of iPhone 6S devices manufactured between September and October 2015 had a battery issue and were eligible for free battery replacement.

Lithium-ion batteries are lighter and offer far more energy density that their predecessors, nickel-cadmium batteries.

A typical iPhone lithium-ion battery should last for approximately 500 cycles.

How you drain and recharge the battery also impacts battery life.

Side reactions in the chemistry increase when you drain the battery to 0% and constantly recharge to 100%. No matter what the charging capacity of lithium-ion batteries will change over time.

Professor Donald Sadoway, who studies material sciences at MIT, said most lithium-ion batteries are engineered to go thousands of cycles and still retain 80% of their capacity.

Temperature, battery degradation and the amount of power being drawn from the battery can all affect that estimate.

Professor Sadoway agrees that there are many reasons why a battery charge meter in the iPhone might be wrong.

Recharge Stanford's Gent reminded me that as lithium-ion batteries degrade, "Determination gets less accurate, particularly when you get close to 0% SOC. So your phone or laptop may think, based on the voltage of the battery, that it has 30% left, but then the voltage unexpectedly starts dropping rapidly and the computer realizes that actually, the SOC is lower than originally thought." This supports my theory that there is actual confusion among the real state of the battery, the hardware's ability to deliver that information to the operating system and the system's ability to accurately interpret it.

"My guess is that the biggest improvement will come from the battery management side rather than the battery tech." The good news, for what it's worth, is that you're not crazy.