Devices with dual battery slots feature an Atomos battery looping technology called Continuous Power. When power is running low on one battery, power is automatically switched to the second battery allowing you to remove the exhausted battery and replace it with a fully charged one. The unit continues to operate as you do this, allowing you to continue recording uninterrupted. Ninja2/Ninja Blade/Samurai Blade battery slots are labelled “1” and “2” – for these models a charged battery needs to be in slot #1 for start-up. For the Flame series and Inferno either battery slot can be used for start-up.