hey guys...any help would be great! just got my Xtreme stock ESC in the mail and saw this in the pics but didnt think about it, is it a cap or BEC and how do i install it, just add it to the POS and NEG wires off the esc when i solder up the battery wires and thats it?

I kno what the wiring is, just not the cap/bec is...im assuming a cap but is it needed with my REVTECH 17.5 motor?