How do I add battery percentage to Home Screen

You may add the large battery widget showing percentage.

Use widgets on your iPhone and iPod touch - Apple Support

Or you may simply find percentage in Control Center or Today view (with a widget).

I don’t know what phone you’ve got but on an iPhone 12 you can pull down slightly from the top right-hand of the screen to reveal battery percentage and a few other things. Or you can use a widget.