Apple makes this process difficult on purpose.
Having replaced batteries successfully on previous iPods, I recently bought a replacement battery for my iPod Classic, with clear and specific directions included, and several Yoochoobs available. However, the process went nothing as advertised, eventually leading to the destruction of said iPod.
Fortunately I had a spare one unused in its box. Back in business.
Apple really does not care one hoot for their customers. Their only saving grace is that their devices usually work well. For a while.