How to fix lag on iPhone 11 after iOS 26.5 update without replacing the battery?

You have already performed all the usual steps, so the answer to your question would appear to be "no".

I do have an older iPhone 11 Pro here and have had no issues with "lag" on the device. But....the battery was replaced about the same time that the iPhone was updated to iOS 26 last fall.

Depending on the current age and condition of the battery......performance might improve with a new replacement battery. But....there are no guarantees.

We might be able to tell you more about whether a new battery might help if you are interested and can provide the current setting for Maximum Capacity on the battery.

Tap Settings > Battery > Battery Health and Charging to see the current Maximum Capacity.

If the iPhone 11 still has its original battery, you already know that it is probably long past due for replacement.

There may be several reasons due to which an iPhone may behave as described by you. Some of them could be...

Let's delve a bit deeper into some of them:

1. Storage: A full iPhone can definitely slow things down. Phones can experience performance issues when the storage is nearly full. Users can check their storage status by going to Settings > General > [Device] Storage. Deleting unnecessary apps, photos, or videos can free up space and improve performance. How to check the storage on your iPhone and iPad - Apple Support.
2. Battery Health: A degraded battery can impact performance. A deteriorating battery can impact the overall performance of an iPhone. Checking the battery health can be done by going to Settings > Battery > Battery Health. If the maximum capacity is significantly reduced, it might be time to replace the battery. Prolong and Maximise Battery Performance … - Apple Community
3. Incorrect Handling: Accidental drops or bumps can cause internal damage. looking at the Apple's guide on proper handling is a good step. Important handling information for iPhone - Apple Support (IN)
4. Environmental Issues: Extreme temperatures, dust, and water exposure can all be detrimental.
   1. Keeping iPhone clean is an important step. Dust accumulation in the iPhone's ports and openings can affect functionality. Apple provides guidelines on how to clean iPhones safely, which usually involves using a soft, lint-free cloth to remove dust without causing damage. Cleaning your iPhone - Apple Support
   2. Keep the iPhone within temperature limits. Phones are designed to operate within a specific temperature range. Exposure to extreme temperatures, especially in parked cars, can lead to overheating or other performance issues. If your iPhone or iPad gets too hot or too cold - Apple Support.
   3. Addressing safety issues is also important: Important safety information for iPhone - Apple Support (IN)
5. Unauthorized Service: Servicing an iPhone through unauthorized channels can result in substandard repairs and void warranties. Users should always seek authorized Apple service centers for repairs and maintenance.
   1. Repairs by unqualified technicians can introduce new problems. Find information about your warranty or AppleCare plan - Apple Support is helpful.
   2. Modification / Alteration of an iPhone by a third-party vendor may cause issues beyond repair. --> Unauthorized modification of iOS - Apple Support (IN)
6. Jailbreak: Now, let's talk about jailbreaking. Jailbreaking removes Apple's restrictions, allowing for more customization and app installation outside the App Store. However, it can also lead to instability, security vulnerabilities, and issues receiving future iOS updates.

By considering all these possibilities, you've provided a comprehensive approach to troubleshooting the iPhone's behavior.

Understanding and addressing these factors can help you maintain the optimal performance and longevity of their iPhones. Following Apple's guidelines and seeking authorized support when needed are crucial for a positive user experience.

If you are sure it is the fault of the equipment.

If you have either dropped the device accidentally or exposed it to liquid or used it beyond acceptable temperature limits then…

Take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support:

Find Locations - Location Selector - Apple

Contact Apple for support and service - Apple Support 

Get a Genius Bar Reservation and Apple Support Options - Apple

Contact Genius Bar.

Manage Reservations - My Reservations - Apple

What is your Battery Health percentage at Setting > Battery > Battery Health?

That is the determining factory if your battery is going to need to be replaced no matter what iOS version you are using. If it is under 80%, there is no other option but to replace the battery or put that money (about $99) into a new device. The iPhone 11 is only expected to last 500 charge cycles before the battery needs replacing and you are correct that there are many older iPhone users that are currently experiencing lag because the battery has needed to be replaced for a long time.

What is the state of the battery? Go to Settings/Battery/Battery Health to find out.

I was not aware that it was a known issue; where did you get that information?

Do you see this messsage on your iOPhione 11:--> Battery health degraded

If battery health has degraded significantly, the below message will also appear:

Your battery’s health is significantly degraded. An Apple Authorised Service Provider can replace the battery to restore full performance and capacity. More about service options…

This message doesn’t indicate a safety issue. You can still use your battery. However, you may experience more noticeable battery and performance issues. To improve your experience with a new replacement battery, get a service.

Do you see this message --> Unable to verify

If you see the message below, it means that the battery in your iPhone is unable to be verified. This message applies to iPhone XS, iPhone XS Max, iPhone XR and later.

Unable to verify this iPhone has a genuine Apple battery. Details from this battery may not be accurate. Learn more...

The battery health information on this screen may not be accurate. To get your battery checked, arrange a service.

JoshuaCM wrote:

i have updated to ios 26.5 on an iphone 11, but i cannot restore from my backup file, as i do not have the password and it is not on icloud. it is a known issue on older model phones to have lag with this update. However, the phone ran better before the update.

Not every issue an individual encounters on their iPhone 11 device can be attributed to an iOS update. If the update itself were the root cause, then every iPhione 11 device running that same version of iOS would exhibit the identical problem. In such a scenario, the forums would be flooded with countless posts reporting the same malfunction, creating an unmistakable wave of complaints that no one could possibly overlook. The absence of such widespread reports strongly indicates that the issue is not systemic, but rather specific to the iPhone 11 in question.

Today, I have tried to sync these to the cloud. I do not have a subscription to the iCloud.

What was the error message that appeared when you tried to sync the Notes with iCloud?

Unless you have the equivalent of many novels stored on the iPhone, syncing the data to the cloud is not going to improve what you are calling the "lag" issue.

JoshuaCM wrote:

Hello. I have a battery at 87% health. It has not been jailbroken or had unauthorized service.

The battery had to have been replaced at some point or the phone was purchased refurbished somewhere. It is highly unlikely an iPhone 11 that was discontinued 4 years ago would be showing a 87% Battery Health on its original battery.

if I have set this phone to only store notes to the phone itself. Today, I have tried to sync these to the cloud. I do not have a subscription to the iCloud.

What happens when you turn on iCloud for the Notes app at Settings > [name on top] > iCloud > Notes?

You don't need an iCloud subscription to sync your notes, you just cannot have greater than 5GB of data already stored in iCloud. You can follow the steps here to view the amount of storage you are using and reduce that storage amount if that is the reason you are unable to sync notes to iCloud.

Manage your iCloud storage on your Apple device - Apple Support

It looks like all of my notes are stored on the phone, and I was unable to move them to the cloud. Is there a way to export them?

You can export each individual note as a PDF, but that is not a backup file where you can restore all Notes when they are deleted by removing the Notes app with them only saved on your iPhone locally.

Export or print notes on iPhone - Apple Support

I have read that I can possibly uninstall the notes app and reinstall it to resolve the lag issue.

I have not seen where the is any issue with the Notes app that would be resolved by a remove/install. That is a basic troubleshooting step that you will find for any app where you are experiencing trouble, but honestly that recommendation sounds like it came from AI instead of someone who has experienced lag with the Notes app. I suppose it is possible if you have a tremendous amount of data (several GB's) used by Notes and maybe even little free space on your drive that is struggling to manage the virtual memory opening a file of that size where Notes would lag, but I don't even think the delete/install would be a solution for that.