Battery drainage on iOS 26 is too high

You are going to need to provide more information to determine why that may be the case.

• What is your Battery Health at Settings > Battery > Battery Health > Maximum Capacity.
• What is your cell signal? More power is required when you have 1 bar compared to a full signal to maintain a connection to a tower farther away. With 5g active, the towers must be closer to maintain that connection. The iOS version does not change the cell signal, but the location would matter.
• Post a screenshot of what you see at Settings > Battery, that includes the green battery graph along with the top apps consuming the battery. If Instagram is on your list, that has already been identified as consuming too much of your battery, but Meta can solve that problem. Apps notes there with Background Activities are using your battery when the app is not opened.

It's not always the iOS update's fault!  Many things can cause phone problems.  If you tell people you think it's an iOS update, it might make it harder to fix or find a solution for the real issue.

Remember, the right question often leads to the solution!

Was/Is your device Jailbroken? If that's the situation, please be informed that attributing the issues to iOS updates may not be accurate.

iOS updates aim to enhance user experience, boost security, and fix bugs rather than disrupt core features. The majority of the issues after updates might stem from underlying, unmentioned factors. Updates won't typically alter personal data but may refine settings or features. Backup before major updates for safety. Review Apple's update details and backup advice for a smooth process.

Kindly consider checking your settings and addressing any device issues before attributing the issue to external factors. This could be a pure coincidence that the iOS update affected the iPhone functions.

Before initiating a standard iOS update, it's advisable to create a backup. Have you completed this step? If yes, proceed with the restoration from the backup.

See what each update does: OS — iOS 26, About iOS 18 Updates, About iOS 17 Updates, About iOS 16 Updates, About iOS 15 Updates, About iOS 14 Updates, About iOS 13 Updates, About iOS 12 Updates, and so on...