If you have an older iPhone,
you can turn on the battery percentage
so it displays in the upper right corner
of the screen all the time.
First, open the settings app.
Tap "Battery."
Toggle on battery percentage to display.
Unlike earlier-model iPhones,
you cannot see the battery percentage
on the home screen of later models.
You can either hook up your iPhone to a charger
and the percentage will appear,
or from the home screen or any open app,
swipe down the upper right corner of the phone.
You should see the control center
with the battery percentage in the corner of the screen.