battery health iPhone 6S 84%

Never heard that behavior.

But... 84% is close to 80% (the suggested limit percentage to replace the battery)... and when the battery is reaching the critical point of its life, it might have sudden / unpredictable behaviors.

I would make a full backup of your device then have your battery replaced at an Apple Store or Authorized Service Provider.

Regards

Giulio

I wouldn’t say it’s phony, but it’s not real time. The only real time reading I know of is from a Mac program called coconutBattery.

https://www.coconut-flavour.com/coconutbattery/

It provides what the developer calls a “defensive” reading which varies at different readingS but overall follows a trend. It also provides the cycle count recorded on the onboard battery diagnostics, and as far as I know the only other way to read the cycle count is through an official Apple diagnostic. I got that with my battery replacement service, and when it was complete the Apple Store employee saw stream of data on his iPad Mini and then authorized the battery replacement.

My last iOS Battery Health reading is 99%. I’m kind of skeptical, but coconutBattery last said it was 98.0% at about 176 cycles. For whatever reason (and I’ve done nothing special) his battery isn’t losing much capacity.

Can’t be too sure what’s the issue with your battery where it’s stuck at 84%, but you could have replaced it during the $29 promotion. My wife got a new battery for her 6s Plus, and it was showing Battery Health at 83%. You could still get it replaced now, but it’s $49.

Gil Woolley wrote:

Based upon a sample of one, I think that Battery Health is phony.

It seems more likely that there is something wrong with your phone. It sounds as if it's time to have Apple run diagnostics.

Genius Bar Reservation and Apple Support Options - Apple

I would say the number isn't updated in real time. I've seen Battery Health jump rapidly (like 94% to 88% in less than a week), suggesting a correction. It's also only an estimate so the way the estimate is done can be inconsistent.

If you're seeing something like that, it's easy enough to get a replacement battery.

Are you sure that's a 6s? A 6s has a battery capacity of 1715 mAh, while a 6s Plus has a battery capacity of 2750 mAh. Never mind - I see it in your sig on your original post.

As far as defining battery capacity goes, that's really a balancing act. Most lithium rechargeable batteries are "overprovisioned" such that it could be safe to use more of the charge range, but where doing do would likely increase how fast it loses capacity. Apple is already doing that to some extent. Going higher or lower into the charge range will affect battery decline. There are some battery systems (like hybrid cars) that might use half of the charge range and where they can literally go tens of thousands of equivalent full cycles by avoiding the high and low charge range.

Apple doesn't really put a constant current into any phone. It's variable, but may be different depending on the power supply. It's supposed to be able to charge at a higher rate up to about 70% charge and then will back off to prevent the battery from overheating, which would increase battery wear. Also - most lithium rechargeable battery systems will stop charging the battery once it's completely charged, and then wait for the charge level to drop to a certain point before starting to charge again. Trying to constantly "top off" the charge of a lithium rechargeable battery is a sure way to reduce the longevity. With 6s Plus, I believe the maximum current it will accept is 2.1A. That's what a newer Mac will provide and a little less than what a newer iPad power adapter will put out. If you're using the 5W (1A) adapter that came with your iPhone, that's going to limit the charge rate during the initial charge, but probably wouldn't during the upper charge range where the charging circuits will typically reduce the current.