You can tell the status of the SlingStudio Battery in several ways:
The SlingStudio Console app also warns you when the SlingStudio Battery's charge is starting to get low: You get onscreen warnings in the Console app when the battery's charge drops down to 20% remaining, and 10% remaining. At this point, you should try to wrap up your recording or connect the battery to AC power.
You can also switch to a different battery, but be aware: Switching a battery power-cycles the SlingStudio unit. Be sure to close your project before switching batteries.
Just before the battery's charge drops completely to zero, SlingStudio alerts you of the situation, stops all recordings, closes your project, and shuts down.