oop http://mypiandi.blogspot.com/2012/12/retropie-sixaxis-over-bluetooth.html says L3 is button 1, otherwise it seems to agree with me.

https://www.youtube.com/watch?v=j_Jk8up_Aqw shows automated ds3 config built into retropie(just need to know where to look), he did mention something about powered usb being better for bluetooth. The controllers themselves are wireless and have battereies on board, so it would be surprising if they could fail due to insufficient power.