you should have a 1yr warranty on your GPS, i picked one of those 478's from GPS4us as well. i called garmin to ask about warranty, and they said as long as you have the ebay receipt and that it shows it was a "Buy it now" auction, you should be good.
i've also read elsewhere that plugging in the GPS overnight might cure the problem. if you take many short trips where the internal battery doesn't have enough time to recharge may cause that problem....
let us know the outcome of your dealings with Garmin.