Help! Precision M6400

i checked youtube vids and ebay, and those m6400's look different than mine !!

pic shows my laptop,  battery seems to need a thick side and a flat side!    what kind of battery do i need?    the ebay batteries were long and thick all the way across like a regular battery !

i57.tinypic.com/opmzid.jpg>

second, next to the battery case here i put in a hard drive on the right...   is that my primary drive, or the secondary ??  and i am looking for the right "caddy" for that one on ebay ??

third, above battery case, is that the space for the other drive?    youtube ones were showing i had to open up the screws to release something, but i dont see any other place to put one except right on top.    which raises the question:    connection!    which caddy or connector do i need?   i am confused by the pics on ebay!  it is not a direct fit with the drive.

so:   which ebay battery do i need, which caddy and connector for each hard drive??

those m6400 vids did not look the same, and the ebay listings are not clear either.