My iPod shows sad iPod

My iPod classic 5th generation worked fine for a solid 10 years until I went to charge it today. I plugged it in it said battery low. I let it charge for a while and came back and now it's showing the sad iPod logo and keeps restarting. Whenever I take it off the charger it stops so is my battery dead and how do I replace it? Also I really want it fixed because it has 6 obsolete clickwheel games on it as well as all of our photo library.