Is iPhone 17 battery health at 91% normal after 301 cycle count?

The battery in the iPhone 17 was designed to go up to 1,000 Charge Cycles before it declines to a Battery Health / Maximum Capacity of 80%......under ideal conditions.

That works out to a 1% decline for every 50 Charge Cycles.

So, your battery has completed 300 Charge Cycles. Divide 300 by 50 equals 6%. The battery started at 100% and should have declined 6% to about 94% at this time under ideal conditions.

At 91%, your battery is declining a bit faster than normal, but 91% is still good performance.

You may do a little better if you set up the battery for Optimized Battery Charging and do not use any Charge Limit settings. Connect the power supply to the iPhone late at night and leave it connected all night......every night.

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

iPhone batteries are designed to retain 80 percent of their original capacity when charged for a given number of charge cycles complete charge cycles under ideal conditions.. See the article for exact details. 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 maximum capacity is not at or above 80%, consider contacting Apple about a battery replacement. --> Apple Service and Repair for iPhone Battery - 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 be unusual battery behavior and 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

The measure of battery health deterioration/drainage is subjective and can vary depending on individual usage patterns. There is no universal standard to determine whether the battery health deterioration/drainage is normal or abnormal because it heavily relies on how the battery is used and maintained.

Protect & Prolong the Life of your iPhone's Battery:

1. About the battery usage on your iPhone, iPad, and iPod touch ...
2. Batteries - Maximising Performance - Apple (IN)
3. iPhone Battery and Performance
4. About Charge Limit and Optimised Battery Charging on iPhone - Apple Support (IN)

• Find out what to do if Optimised Battery Charging doesn’t activate.
• Find out what to do if your device stops charging unexpectedly.
• Find out what to do if you think your battery is draining too quickly.
• Find out how to charge and maintain your iPhone battery.

Try to monitor Battery usage by iPhone Activity as shown below

What is shown under battery usage? Checking that would give you an indication of the usage behavior.

1. Background Activity
2. Notifications
3. Connected to Charger
4. Or any Other

Try some of these options too.

To prolong the life of your iPhone battery, you can follow these tips and best practices:

To prolong the life of your iPhone battery, you can follow these tips and best practices:

1. Optimize Battery Charging: Enable the "Optimized Battery Charging" feature on your iPhone. It helps reduce the wear on the battery by slowing down the battery aging process. You can find this option in Settings > Battery > Battery Health. About Optimized Battery Charging on your iPhone - Apple Support (IN)
2. Avoid Extreme Temperatures: Extreme temperatures, both hot and cold, can negatively impact your battery life. Avoid exposing your iPhone to excessive heat or cold, such as leaving it in direct sunlight or in a freezing car.If your iPhone or iPad gets too hot or too cold – Apple Support (UK)
3. Use Original Chargers and Cables: Always use Apple's original chargers and cables or certified third-party accessories. Low-quality chargers or cables can damage the battery and reduce its lifespan. Identify counterfeit or uncertified Lightning connector accessories - Apple Support (IN)
4. Avoid Draining the Battery to Zero: Charge it whenever the charge becomes lower than 20%. The rest is up to you when to charge. how long to charge, how often to charge, which adapter to use starting from 5W to 140W USB-C Power Adapter etc.
5. Optimize Display Settings: Adjust your display settings to optimize battery life. Lower the screen brightness, enable auto-brightness, and use shorter screen timeout durations. Adjust the display and text size on iPhone - Apple Support (IN)
6. Minimize Background App Refresh: Limit the number of apps allowed to refresh in the background. Go to Settings > General > Background App Refresh and disable it for apps that don't require real-time updates. Switch apps on your iPhone, iPad, or iPod touch - Apple Support (IN)

I agree with Bob Timmons that your battery while still normal, has degraded very slightly faster. There are just so many factors which contribute to Battery Health decline. Letting the battery fully deplete can age the battery faster. Routinely using the phone when the charge is below 20% can also age a battery faster.

Read this and open the embedded links inside it to learn more about battery charging best practices --> Battery Health Decline - Should You Worry… - Apple Community