I tried with my 505 and although the instructions were good, apparently my technique wasn't so great and I slightly nicked the ribbon tape that controls the buttons (apparently that happens often according to forum comments I've read) making my reader inoperable. That made it the most expensive battery ever because I had to get a new reader AND I had paid $35 for the battery and shipping, which was then useless... As long as you realize that it "may" not work out and are OK with it, it's worth a try.
The site where the videos are posted is the one for the battery supplier:
http://www.newpower99.com/Sony_Porta...%20prs-505.htm