So I wanted a magic box for my EP121 This box is the size of the EP121 length and width so the device can sit on top of it easily (perfect for an airplane food tray) or the box could easily fit in a backpack behind the EP121. The box would provide an extra 8-12 hours of extra battery. The box would not require too many extra cords to carry around - just the box. Here's what I ended up with A 3D rendering of the project idea A top-down size comparison of the EP121 laying flat on the box The Energizer XP18000s and their power supplies in the box I know - bad Photoshop. My 2nd XP18000 is in the mail Finished box with both cord straps open and cords exposed Note: There are two holes in the top yet to be cut for access to the battery status and 'on' button on top of the XP18000) Access port for USB charging (usually hidden under velcro strap) Basic wiring diagram (XP18000s are in parallel) This also replaces the need to carry around the EP121s own adapter since the power supplies for the XP18000s can charge both themselves and the EP121s internal battery simultaneously. What do you all think? Nice accessory for the EP121 or ridiculous pet project?