Rapid decrease of battery health

2% per month is not unusual, plus the determination method is an estimate.

To learn about maximizing (and the difference between) battery life and lifespan, read this support document --> Batteries - Maximizing Performance - Apple

Read this support article about iPhone battery and performance to learn about the battery health feature and what is considered normal performance --> iPhone battery and performance - Apple Support

To see the feature go to: Settings > Battery > Battery Health

"A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions. The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge." A degraded battery may display the notice: "Your battery’s health is significantly degraded. An Apple Authorized Service Provider can replace the battery to restore full performance and capacity." If it is not at or above 80% "normal", consider contacting Apple about a battery replacement. --> iPhone Battery Replacement - Apple Support

According to the above quoted information, you could be losing almost 2% per month the entire first year before Apple would deem this to merit a warranty replacement.

Also read:

- Apple’s support article about batteries draining too quickly —> If the battery in your iPhone or iPad drains too quickly - Apple Support

- This post by ASC contributor Lawrence Finch which has a very user-friendly explanation of battery features --> Bettery health maximum capacity - Apple Community

At 35 Charge Cycles, the battery should be at about 99%.....maybe 98% if there was a lot of data that you transferred from another phone or backup.

At 250 Charge Cycles, the phone should be at about 95% and about 90% at 500 Charge Cycles. Unfortunately, even if the battery is declining faster than normal, Apple will not replace the battery unless the Health drops below 80% in the first year of operation.

So, there is not really anything that you can do at this point other than continue to use the phone. If the battery continues to decline rapidly, there is a point where you may likely start hoping that the Health drops below 80% at about 11 months, so you will get a free battery replacement from Apple.

It might be another discussion, but in my opinion Charge Limits are more of a gimmick than anything else. My recommendation would be to ignore the limits and set up the battery for Optimized Battery Charging and connect the phone to the power supply at night and leave it connected all night....every night.

 The biggest enemies of battery health are heat and frequent full charge cycles. When you use fast charging, your phone generates more heat, which accelerates battery wear. While modern devices include safeguards to manage temperature, consistent exposure to high heat still shortens battery lifespan over time.

No matter how carefully you treat it, every lithium-ion battery will degrade eventually — it’s a normal part of chemical aging. However, you can significantly slow down that process by following a few key habits:

• Avoid excessive heat. Keep your phone out of hot environments and don’t use it heavily while charging.
• Limit full charges. Try to keep your battery between 20% and 80–85% for daily use.
• Use fast charging sparingly. Rely on regular or optimized charging when possible.
• Enable battery optimization features. Many phones can automatically slow or stop charging around 80% overnight.

In short: you can’t stop battery degradation — but you can manage it. Keeping your device cool and avoiding constant full charges are the most effective ways to extend your battery’s life.

Battery health decline is inevitable but not linear, it may not decline so fast in the coming months.

If it drops to 79% inside the Apple warranty you should get a new battery for free, but I doubt that will happen. No other guarantees apply

Restricting to 85% charge will not extend battery life, it will simply reduce the battery you have left for that day, it is a gimmick for worried users.

Charge to 100% every night all night with optimised charging on.

IdrisSeabright wrote:

from0toHero wrote:

• Limit full charges. Try to keep your battery between 20% and 80–85% for daily use.

It is my understanding that that advice is not accurate or necessary.

When to charge your iPhone or iPad - Apple Community

Yes, it is a myth, pandered to, for the worried well, by Apple's new charge limit. My phone does not support charge limit, so it can't be that important.

Charging to 100% every night all night, and running down to 10% if necessary, will not damage battery longevity. It is purely down to charge cycles and or excessive heat.

from0toHero wrote:

• Limit full charges. Try to keep your battery between 20% and 80–85% for daily use.

It is my understanding that that advice is not accurate or necessary.

When to charge your iPhone or iPad - Apple Community

from0toHero wrote:

...

In short: you can’t stop battery degradation — but you can manage it. Keeping your device cool and avoiding constant full charges are the most effective ways to extend your battery’s life.

Keep cool, yes

Avoiding full charges, for iphones, no, myth.