The Octamount fits into a node socket on the OpenBCI Ultracortex EEG headset. It can accommodate the OpenBCI board holder or the battery trays included in this kit. It also fits some other generic battery cases without a tray (using the provided screw holes). One of the trays fits the 4xAA battery case that comes with the OpenBCI boards, and the other trays fits the common LiPo batteries available from Adafruit in 2500, 2000, and 1200 mAh capacity, since those batteries are too large to fit within the OpenBCI case (The 500mAh LiPo is normally used). See this blog post for other high-capacity battery options for OpenBCI headsets: Powering The Ultracortex