Ipod Classic Battery Drains Fast Only During Sync

Hello. I bought a ipod 5th 30gb generation video i think its called? from my friend for 35$ And i took it home and noticed it was dead. So i charged it overnight. Then in the morning it was plugged in and working! I unplugged it and connected it to my laptop to sync. As i was syncing i noticed the battery drained SUPER FAST. So it died with only like 15 songs in it out of my 1,000+. So i charged it halfway this time. And DID NOT plug it in to my computer to sync. The battery has been lasting. But i tried to sync again and then the battery drained fast again only when syncing? Im confused and concerned. Why is it doing this? Should i get my money back from my friend?

Thanks