Are you just realising this?
Welcome to the wonderful world of 'chipods'!!
No one should expect to get a perfectly working mp4 player for such a low price. Anyone who does would have to be a fool.
I've had a cheap piece of cr@p for almost 3 months now and i love it. It's slow and stubborn as a mule but it gets the job done. Worth every penny of the $50 i paid and i would not swap it for a $250 iPod Nano.
Why?
Because they can't play videos, you have to muck around with iTunes to get music on it, it'll only play Apples preferred formats and it costs an arm and a leg to repair or change the battery.
I can change my old battery for a longer lasting one for about $10 and double or triple my play time, but i've never lost the contents of memory when the battery was so low it wouldn't turn on. I've made a custom 'Docking station' for my computer (thanks to Joffas design

) that i plug it into at night and give it a top up charge while i'm sitting here.
I know what to expect when i buy, and steer way clear of Ebay.
I've got a few for my friends and they love them too so this whole 'chipod' thing isn't really new for me.. call it a 'hobby'