I presume you know about
PRS+. If not, here are two additional helpful links:
http://www.anamardoll.com/2011/06/er...tion-with.html
http://erhartc.bplaced.net/ereader/index.php
EDIT: I've never heard of any stability problems with PRS+. I have it on my PRS-350s, and am thinking of putting it on my 505.
Back when the 505 was new, I recall threads here of people who couldn't charge via USB, and it was concluded that an A/C (mains) charger is required. Sony's OEM charger was expensive, but any charger made for the Sony PSP will do just as well.