Apple has "Optimized Battery Charging". Exactly why does it help?
March 29, 2021 6:37 AM   Subscribe

Details inside.

Apple says (here): "Optimized Battery Charging is designed to reduce the wear on your battery and improve its lifespan by reducing the time your iPhone spends fully charged."

It's easy to understand what it does because they explain that very well (here). Fast charge to 80% then slow after that. Uses artificial intelligence to predict when user will need it to be at 100%.

Also, they explain (here) very well that a battery's charge capacity is reduced a bit by factors including extreme cold and heat and its number of "charge cycles", each of which occurs every time accumulated discharges and recharges of the battery add to 100% of its capacity.

So, my question is not about those things, or about overcharging, which I assume all their new phones are able to prevent.

I'm asking about exactly why "reducing the time your iPhone spends fully charged" will "reduce wear on your battery and improve its lifespan"?

What is it about the battery being fully charged that is bad enough that they want to reduce the amount of time that it is?

Is it simply that the battery's temperature gets raised by being charged to full, and they're trying to reduce the time that the battery experiences that heat? If so, please explain more about that because that's only a guess, and I don't really understand the why-parts of that either.

Please share links.

posted by atm to Technology (7 answers total) 6 users marked this as a favorite
Overheating plus maximum charge cycle limitations I believe. Brief (non-technical) write up
posted by Hartster at 6:43 AM on March 29, 2021 [1 favorite]

Best answer: From this electronics industry article:

Permanent capacity loss, as the name implies, refers to permanent loss that is not recoverable by charging. Permanent capacity loss is mainly due to the number of full charge/discharge cycles, battery voltage and temperature. The more time the battery remains at 4.2 V or 100% charge level (or 3.6 V for Li-ion phosphate), the faster the capacity loss occurs. This is true whether the battery is being charged or just in a fully charged condition with the voltage near 4.2 V. Always maintaining a Li-ion battery in a fully charged condition will shorten its lifetime.
posted by zsazsa at 7:29 AM on March 29, 2021

Best answer: Not sure why this website isn't working, but here is a great explanation. It's not about heat, it's about battery degradation happening outside of the 20-80% range.

Here's a research topic they quote.

Here's an article again about how LIION batteries die through this process. - again, sorry for cached.



During charge, lithium gravitates to the graphite anode (negative electrode) and the voltage potential changes. Removing the lithium again during discharge does not reset the battery fully. A film called solid electrolyte interface (SEI) consisting of lithium atoms forms on the surface of the anode. Composed of lithium oxide and lithium carbonate, the SEI layer grows as the battery cycles. The film gets thicker and eventually forms a barrier that obstructs interaction with graphite. (See BU-701 How to Prime Batteries)

The cathode (positive electrode) develops a similar restrictive layer known as electrolyte oxidation. Dr. Dahn stresses that a voltage above 4.10V/cell at elevated temperature causes this, a demise that can be more harmful than cycling a battery. The longer the battery stays in a high voltage, the faster the degradation occurs.

The buildup can result in a sudden capacity loss that is difficult to predict by testing the duration of a battery through cycling alone. This phenomenon had been known for some years and measuring the coulombic efficiency can verify these effects in a more scientific and systematic manner than mere cycling.

Similar to an EV, Li-ion in satellites must also endure a lifespan of 8 years and more. To achieve this, the cells are charged to only 3.90V/cell and lower. An interesting discovery was made by NASA in that Li-ion dwelling above 4.10V/cell tend to decompose due to electrolyte oxidation on the cathode, while those charged to lower voltages lose capacity due to the SEI buildup on the anode."

So, in conclusion, the higher the voltage on the battery, the more it degrades. So, by keeping the battery from 100% for 8 hours a day (when it's gently discharging/recharging) it should take it out of that "worse degradation period" for 1/3rd of it's lifespan.
posted by bbqturtle at 7:34 AM on March 29, 2021 [4 favorites]

Response by poster: Awesome, guys!

Thanks very much!
posted by atm at 7:52 AM on March 29, 2021

Great clear answers — which raise some concerns about laptop use in this household.

My wife and I (both WFH over the last year) have our laptops docked in the home office well over 95% of the time. Every once in a while I will need to take mine out and work elsewhere in the house when she’s on a call, but hers has been docked just about the entire time she’s has it. (She uses an iPad or her phone for reading and emailing elsewhere in the house.)

Mine is a win10 Lenovo; hers is a newish MacBook Pro. If the battery technology here is basically the same as phones, is this killing the battery, and do modern OSes do anything to take this into account?
posted by sesquipedalia at 8:26 AM on March 29, 2021

If she is running the latest OS (Big Sur), then the same sorts of battery management stuff is happening.
posted by sideshow at 9:49 AM on March 29, 2021

sesquipedalia, yes, the same things apply. It is definitely better to run off battery power and not keep it at 100% all the time. I keep my computer docked 99% of the time and even after some tiny number of cycles (a few dozen?) it swelled up and had to be replaced. I wish it would maintain it around 50%, enough to run for a while un-docked, but not so it's fully charged all the time. One thing to keep in mind is that all these capacities are relative. In a phone (or worse, a drone) where weight is really important and the design life is only a couple years, you might choose to put the "100%" charge at a higher absolute point in the battery, or put the "0%" further down into the possible range. These would lower the number of cycles that the battery will survive, but increase the available charge. On the opposite end, in cars, where even a modest range reduction can be a major problem (40 miles range on a Leaf might not get you to work if it turns into 30 by year 10), the tendency is to use only the gentlest center of the theoretical charge. Laptops are somewhere in the middle. I think all you can realistically do is make sure you have plenty of ventilation, especially underneath, and run it on battery power from time to time.
posted by wnissen at 10:08 AM on March 30, 2021

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