Ipod clasic wont stay charged

I have A Ipod clasic its about 3yrs old I got it for my kid and she only used it with the plug. After a deal for the Ipod touch she gave it back. I'm noticing that the battery dosn't stay charged very long. I dont the the age is the issue because I had the 40G for years and never had a problem with it (not until someone stole it that is)

Has anyone found a fix for this problem?