Why doesn't my 3DS hold a charge for very long?

Basically, I used a charging cradle to charge my 3DS. It worked for a while, then it just stopped charging. After about a year, I tried charging it because I was bored. It worked, but it only held a charge for about 10 minutes before dying. I'm going to try getting a new battery, but if that doesn't work, what do you think I could do? It would be great to have a handheld system to play again!