8gb spd and Gerber memory stick confusion

I am upgrading my hp envy 15 from 1 8gb ram stick to 2 sticks but I am confused in the designations marked on my current memory chip. It reads out as "8gb 2rx8 pc3l-12800s-13-fp". Does the 13 and fp matter or can I get a stick with different numbering? What would you suggest getting to double the ram?