Will iOS 26 battery life eventually improve?

Yes, see this

If you notice that your battery life has decreased after updating your device, wait a few days and then check again.

Even though you can use your device immediately after an update, certain tasks related to the update continue in the background and might affect battery life and thermal performance. While they're ongoing, you might see the Insight Ongoing iOS Update in Settings > Battery.

kakyev wrote:

I updated mine last night and turned it on at 6:30 this morning and at 11:30 I started a text and it shut down because the battery died. I have the 17 pro max

Did you leave it on the charger overnight? After the update, the phone will continue the set up process by indexing the files and optimizing your photo library to take advantage of object detection algorithms. This will be performed in the background where you will see lag, battery draining, and the device may even feel warmer than usual for the next several days. Check out the Apple support article here for what you should expect.

About Apple software updates - Apple Support

After 2 days, my iPhone 15 Pro was back to all day battery life. Previously I experienced battery drain after the update where I also had to charge it during the day, but that is no longer the case. I had long ago removed Social Media apps that were the biggest source of my battery drain when I was on iOS 18.

I installed five days ago and the very same nine-mile walk (three hours exactly) that I take every morning, starting with a 100% charge is at zero or near zero. Two days my phone conked out with no charge at all. With iOS 18.x (the latest iOS 18 version) my iPhone 15 Pro Max showed between 40% and 45% after walking 12 miles (about 4 hours); usually around 50% for the usual nine-mile walk.

That is a HUGE drain. I am getting no improvements and I have done everything possible to preserve charge. I am listening to an audiobook (Audible, about 2% battery usage) and checking my distances a few times a mile to assure that I am on track distance-wise. Other than Maps and Apple Health, Mail and Messages takes less than 2% of the battery during my walk.

Apple Health is hogging the battery and it is shorting y distances by about 15–25%. I walk a steady 3 mph and it is crediting me with about 2.25-2.5 miles. All permissions are given to Apple Health to correctly measure my distances. It is the same walk I have taken every day for years. I know what should be showing up. But it is not.

Anyway, with not enough battery charge to walk, iOS 26 is just about useless to me.

I hope they fix this mess. I'd like the option to turn off the animations and turn off completely the transparency. It looks fine, but I'd rather have enough battery to take my walks.

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Why don’t you charge to 100%? I do and have done so for about 5 years. No problems with any of my batteries.

I updated mine last night and turned it on at 6:30 this morning and at 11:30 I started a text and it shut down because the battery died. I have the 17 pro max

After four days, my iPhone 15 Pro Max battery life has not got back to normal yet. In Low Power mode, it works up to 40 hours. With iOS 18.6.2 I could use it as long as 60 hours, depending on the tasks I solved.

IOS 26 tells me my iPhone 15 Pro Max consumes almost the same amount of energy as it did before the update. But the battery life has dropped from 55 to 60 hours to almost 36 hours (on Low Power mode) by now. I hope Apple will release an update to fix the issue soon.

Nine-day follow-up:

Still having significant battery drainage. I reduced all motion/animations in Accessibility. And I turned OFF Adaptive Power as it was limiting Location Services and therefore Apple Health mileage updates (that never were "credited" to my daily totals although I must have walked closer to 12 miles while only being credited for 9 miles). If this is Apple Intelligence, it is not learning very precisely or quickly. Wish there was a a way to tell it that I will be walking nine miles every morning between the hours of X a.m. to X+3 hours a.m.

The only thing that seems to work is to stop and re-charge the battery to over 90%. This is quite a quandary.

I do hope there is an update/patch soon.

For a 15 this is very long.

I ditched my 15 pro because I needed to charge it 3 times a day!

Maybe, but the battery life has dropped significantly. It's a fact.