When my iPad needed a new battery, I bought one on e-bay. I also had to buy an adhesive package and small tool set.
The battery is placed flat against the screen. That means everything just about has to be removed to get to it.
I watched a YouTube video on how to replace the battery. It wasn't easy because the parts are small and the wires are delicate, but I did it.
After that, I just bought a new iPad and kept the old one as a spare. Would I do it again? probably if the battery was the only issue.
Apple wants people to replace, not repair. They will, however, give you credit for your old iPad if you want a new one. Info is on their site.
They will give you a quote on line, send you a shipping box with free postage and issue you a credit for a new one when you send yours in.
You need to backup your pictures and info you want to keep before you return it or you will lose all your stuff.