My iPhone 17's battery is draining so fast without usage

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)

When your iPhone isn't in use, it still drains battery as there are plenty of background tasks always running, such as notifications, widgets, background app refresh, and more.

Also, you should be charging your iPhone all night, every night as a habit. If you don't charge your iPhone overnight, that explains the battery drain into the next day. Allowing your iPhone to charge overnight with Optimized Battery Charging, which is safe for the battery, allows you to wake up with a fully charged iPhone. In addition, your iPhone's background tasks and indexing happen mostly on charger, so if you aren't giving your iPhone that adequate time, it has to find other time to do it, which can be inconveniently when you are using your iPhone and cause it to drain more battery.

About Charge Limit and Optimized Battery Charging on iPhone - Apple Support

I think that’s what the 17 is facing I had the same 17 it drains heavy when siting idle untouched and, it even drains when I put it in airplane mode. And it even drains when I shutdown it down completely

I have been charging overnight connected to a strong Wi-Fi network and when I unplug it can be idle for 2 hours without a single drop of battery but the moment a single battery drops and it drains hard you will check the battery chart and find nothing on the usage and all my background app refresh is off , email push notifications is on fetch manually, I have turned off Always on display like I have did everything necessary but still experiencing the issue