Battery life of all devices

Presumably you refer to the iPadOS Battery Widget...

Add, edit, and remove widgets on iPad - Apple Support

Me-Marie wrote:

At one time, I had on my iPad home screen, the battery life of my iPad, iPencil, iWatch and iPhone in one app. Somehow it’s gone and I don’t know how to get it back…

Apple never offered that. Some add-on app installed on all of the devices might have offered that.