I recently rapidly ran down the battery in my iPhone 13.
I turned on the magnifier to look at something, placed the iPhone face down for several hours and never turned off the Magnifier. Apparently Magnifier does not turn off after some time limit.
In about two hours Battery went from about 80% to 2% of charge.
Live and learn,
Gil Woolley
Wait…what?! Dang, how long has that been there? Thanks! I had no idea it even existed. 
Jeff,
I am 86 years old. A magnifier is very handy.
My old iPhone 6S has a separate app for magnifier.
My newer iPhone 13 I access magnifier by swiping downward right top to left bottom and look for a symbol which looks like a magnifying glass with + sign in the middle.
However, you have to turn Magnifier on. Go to Accessibility and scroll all the way down to Accessibility Shortcut and scroll down again to Magnifier and click on that to turn it on.
Text alone does not explain this well. I found a Youtube video helpful by typing in iPhone 13 turn on Magnifier.
Just FYI, now that you have set an accessibility shortcut, you can access the magnifier by triple-clicking the side button as well as use the magnifying glass icon in control center (which is the screen tat opens when you swipe down on the right side of the notice from top to bottom.)
I have a physical one on my desk that I use frequently. But I was unaware of the existence of the iOS Magnifier app until your post. Apple’s support document on the app lists a whole bunch of other cool tricks it can do.
Thanks!
The Magnifier app is very handy for all the microscopic printing that tech companies seem fond of using on various power supplies, devices, etc.
I do have a dedicated magnifier on my desk. But I am not always at my desk. But, I am a man, my iPhone is always with me except in the shower. Instructions on paint and glue containers are always too small for my eyesight. And my iPhone and the Magnifier app are always with me.
I love that I can access Magnifier through Control Center. I’ve just always wondered why Magnifier can be selected there, but not Measure. Seems to me both apps are very similar.
Another related feature that I use all the time to aid my aging eyes is also in Accessibility: Zoom. When that’s turned-on, I can just double-tap with three fingers and a section of the screen gets magnified, so I can read all that tiny text in any app.