ios 26 upate 16 pro max

For a few days after a major iOS update, our phones are working hard behind the scene to index the millions and millions of bytes of data. That said, did you Force Restart your iPhone after you updated? I do this after EVERY iOS update and I'd recommend you do the same --> Force restart iPhone - Apple Support

I had NO excessive battery drain after updating either our 16 Pro or 16 Pro Max.

Hello,

With any new version of iOS there are always maintenance and reindexing tasks to be performed. It should settle down in a few days.

1) Have you tried a restart?  If not, do it now.

2) Go to Settings > Battery > BATTERY USAGE BY APP to see the apps that are consuming your battery.

3) Check “Battery Health” in the link: 

iPhone Battery and Performance

Good luck.

Additional battery drain when making the update is normal. See this support document from Apple about updates. About Apple software updates - Apple Support