That's too bad about your experience. Did you know that you can
change the battery on the Sony yourself ? (<-- step-by-step how to video also)
I was gifted a 505 on Christmas 2008 and it has been on since then. I charge whenever it is at 3/4 battery. On average, I charge it about every 2 weeks and use the wall charger as it is quicker and more reliable for me.
My mom purchased a 505 also in 2009 and charges her 505 about every 3 weeks.
Did you try a wall charger? Sometimes it takes a full overnight to register a charge.