The camera battery may take a few discharges,before the battery is calibrated. During calibration your battery level may not reflect the actual remaining capacity. This shouldn't take more than 3 full cycles for an accurate reading.
The camera battery will last up to 6 hours on a single charge. There are multiple ways to check your level of charge:
The indicator lights on the back show 25% per light. When not plugged in you can check these lights by pressing the power button once.
When at the Homescreen inside the Mevo app
At the top of the Settings page in the Mevo app