I have an iPod Classic 5th gen 160 GB model MC297C (uses thin battery) bought late 2010. A full charge was giving me only about 45 minutes of music, so the new battery has allowed me to revive my iPod Classic.
I got in Oct 2017 the NewerTech 580 mAh battery replacement kit, extra plastic pry tools and the iSesamo tool and had them shipped to Canada duty and taxes paid, so they arrived within days.
I installed battery Nov 2017. I used anti-static mat and wrist strap. It took about 2-1/2 hours to pry off back cover. Way tougher than changing RAM and installing SSD in my Mac. The rest of job i.e. changing battery and replacing cover took only about 30 minutes; YouTube videos were useful for explaining how to safely disconnect ribbon connector (I think I used a mini screwdriver for this).
I had a total of 6 plastic pry tools and they barely helped to maintain apart the sections that I had managed to unclip. Their curved end gets easily damaged and put out of action. The iSesamo is indispensable if you want to be able to undo the approx 11 clips without becoming totally frustrated and doing something imprudent which may damage the iPod. It worked so well that the only damage I can notice on the casing are scratch marks on the metal sides of the iPod. They should include the iSesamo as part of kit and simply increase the kit price.
Be aware that the battery loses its charge quickly over the course of a few weeks while sitting unused. For a newly installed battery, if it has been freshly recharged (within last 7 days) you can listen to music for more than 4-1/2 hours. If it was recharged 3 weeks ago, you will get barely over 1 hour of music.