At what maximum capacity percentage should I consider changing the battery on my 6-S Iphone

The 80% threshold that others have stated is pretty much the industry standard to determine if a rechargeable battery is "depleted". However, just because it drops from 81% to 80% doesn't really mean that much. It's just an arbitrarily round number. Battery health readings are only an estimation, so they can be incorrect with older batteries.

80% used to be the threshold where Apple would be willing to perform a battery replacement service. However, with the current worldwide battery replacement promotion, there's no requirement that it be under that threshold. If you really want a new battery you can request it one time at the current price, even if it's still reading as healthy (over 80%).

Apple considers batteries to be in acceptable condition down to 80% capacity.

Actually, the Apple threshold is it should retain up to 80% of its design capacity at 500 cycles (iPhone Battery and Performance - Apple Support). So if someone’s battery were to test (by Apple) at less than 80% and less than 500 cycles within the one year warranty period, that would be considered premature failure and indication of a bad battery. That would be replaced under warranty at no charge.

Some batteries will retain more than 80% of design capacity well after 500 cycles. That‘s why I say to go by how it’s actually working. Percentage of retained capacity and cycles really don’t matter if the battery is no longer useable to the person using the device. Similarly they don’t matter either if the capacity is fine for someone’s regular usage pattern between charging.

People get so hung up on monitoring these various numbers and they‘re largely pointless. Does your battery work well enough for you now? That’s really all that matters, regardless of some firmware algorithm’s computed capacity values.

Are (most) people daily checking their car battery‘s voltage, current and electrolyte specific gravity? No. When it eventually starts struggling to crank your car‘s engine you replace it. Until then, you just go on using it. Every single chemical battery people use or have ever used experience analogous degredation in capacity with age and use, yet nobody cared one wit about retention capacity or cycles before SMART lithium technology made it easy to estimate such things and display them for users.

Michael Black wrote:

Quite honestly, I wouldn’t pay any attention to the percentage itself. Does the battery hold a charge long enough for your use - yes or no? If you‘re finding that the capacity is nowhere near enough to last you for your normal day’s usage, then it may be worth checking it with Apple and see about a new battery. But if it’s lasting acceptably long enough for you, then what difference does the percentage of original capacity remaining matter?

I absolutely agree. While the new Battery Health item in settings is very useful, I think it's causing a lot of people to pay undue attention to the number.

Michael Black wrote:

Actually, the Apple threshold is it should retain up to 80% of its design capacity at 500 cycles (iPhone Battery and Performance - Apple Support). So if someone’s battery were to test (by Apple) at less than 80% and less than 500 cycles within the one year warranty period, that would be considered premature failure and indication of a bad battery. That would be replaced under warranty at no charge.

I get that. However, 80% and 500 are still just round numbers. 500 might be more in line with test results, but that it's set at 500 for all current iPhone models can't be because it's some absolute. It's 1000 for iPads and Mac notebooks. Once it hits that magic number it doesn't just suddenly turn into a pumpkin any more than a car is any less useful when it hits 100,000 miles. But Apple has those as their parameters for expected longevity, and as you state they work that into warranty replacement eligibility.

People get so hung up on monitoring these various numbers and they‘re largely pointless. Does your battery work well enough for you now? That’s really all that matters, regardless of some firmware algorithm’s computed capacity values.

I understand that. It's almost a sense of pride that someone could get a battery to last longer than average by doing all these little things that might possibly result in slower degradation. Stop charging at 80%. Never let it go under 40% or maybe 20%. Only use the 5W power adapter. But in the end it's just to extract a little bit more life out of a battery that costs $29 to replace right now.

I remember back in the early days of Apple's forums, people were bragging about how their battery health was going up like they actually did something to restore lost capacity.

Quite honestly, I wouldn’t pay any attention to the percentage itself. Does the battery hold a charge long enough for your use - yes or no? If you‘re finding that the capacity is nowhere near enough to last you for your normal day’s usage, then it may be worth checking it with Apple and see about a new battery. But if it’s lasting acceptably long enough for you, then what difference does the percentage of original capacity remaining matter?

IdrisSeabright wrote:

y_p_w wrote:

Stop charging at 80%. Never let it go under 40% or maybe 20%. Only use the 5W power adapter. But in the end it's just to extract a little bit more life out of a battery that costs $29 to replace right now.

Because someone who is new to these forums might not plow through your rather dense posts to discover that you weren't necessarily endorsing them, I want to make it clear that none of those procedures are necessary.

Those are procedures that have been discussed here before. Even Lawrence says he'll only charge overnight with the 5W adapter. If someone is asking if they will help increase longevity, the answer is yes, but at the cost of convenience. And only to extend the life of something that's inexpensive to replace.

y_p_w wrote:

Stop charging at 80%. Never let it go under 40% or maybe 20%. Only use the 5W power adapter. But in the end it's just to extract a little bit more life out of a battery that costs $29 to replace right now.

Because someone who is new to these forums might not plow through your rather dense posts to discover that you weren't necessarily endorsing them, I want to make it clear that none of those procedures are necessary.

Modern batteries can be charged as needed. The only caveat is that they should not be left in an uncharged state for extended periods.

Lawrence Finch wrote:

It’s true that I charge my iPhone with a 5 W USB adapter overnight, but that’s because my 12 W adapter is charging my iPad overnight. And I’m not in a hurry.

So, suggesting that you advise against charging your phone with an 12W adapter is inaccurate? 😉

In the course of my previous job, I acquired a couple of extra 12W adapters. so, I tend to just use those. But, that's because I tend to lose the smaller 5W adapters.

IdrisSeabright wrote:

So, suggesting that you advise against charging your phone with an 12W adapter is inaccurate?

😉

In the course of my previous job, I acquired a couple of extra 12W adapters. so, I tend to just use those. But, that's because I tend to lose the smaller 5W adapters.

I don't recall ever saying to not use the 12 W USB adapter. And I have frequently provided links to Apple's page for it that states that it can be used for iPhones, as well as just about any Apple mobile product. Apple 12W USB Power Adapter - Apple

Click on "Compatibility"

You are replying to the champion of unnecessary cruft in the ASC.

deggie wrote:

You are replying to the champion of unnecessary cruft in the ASC.

Yup.

It’s true that I charge my iPhone with a 5 W USB adapter overnight, but that’s because my 12 W adapter is charging my iPad overnight. And I’m not in a hurry.

I didn't recall that you had, either.