So I finally got the Energizer XP18000 battery to work with the EP121 (after adding an inline barrel plug to the EP121 charger so I can use the plug it shipped with on both the charger and the XP18000) Here is my benchmark. Full brightness. WiFi on. Bluetooth off. Looping 720p video. Note: XP18000 status is marked by how many of the 4 status lights turns on when I press the button 0:00 EP121 @ 90% XP18000 @ 4/4 1:00 EP121 @ 100% XP18000 @ 2/4 3:10 EP121 @ 100% XP18000 @ dead 5:23 EP121 @ Auto Shutdown (3%) XP18000 @ dead Hope this is useful to someone. Keep in mind that this is a very worst case scenario.