I haven't used my 3G iPod much in recent years, but I noticed it had no battery life left. I could charge it, but it wasn't holding the charge.
I've used iFixit guides to upgrade memory and a hard drive in my Mac Mini, and the 3G iPod guide was just as accurate (meaning, very good). When they say you need to be patient in your efforts to open the case, they mean it. I knew once I got the first tab loose, the rest would follow easily. Getting that first tab loose was a challenge. The iPod kept slipping from my hands, and twice it bounced to the floor.
Keeping a grip on my iPod was the toughest thing. The large iPod plastic tool broke, so I had to get creative with some other tools I had to help me get that first tab loose (Eyeglass screwdrivers helped in the pinch but scarred the case just a little--not noticeably). Once I got the case separated, the rest of the job was easy. Replacement and reassembly were a breeze.
The iPod has charged and is playing just like new with a nice charge on the battery.
Patience and determination are your friend for getting the case apart. I did not need the T6 Torx screwdriver (forgot all about it until after I had the case reassembled), but it will be handy to have for other jobs.