The logic board which hold the charging unit is what goes bad. I dont know what causes it but i have seen a few cases where the battery just wont charge. its a hit or miss but the logic board would be the first place i would check. in all my cases it was just a matter of replacing the logic unit. BEFORE YOU go and order a part and try to fix it just look inside the charing port of your iPod and make sure there nothing in there.. sometimes its just a piece of lint stuck in there. =) iPod Video (30 GB) Logic Board
Tip* "ONLY WITH METAL SPUDGER* heat it with a lighter till its warm to touch, then slide it like a butter knife. it reduces chances of chipping glass.