With the default 320mAh battery provided with the system is approximately 4h in continuous operation, considering the use of the Bluetooth interface which accounts for 50% of the power consumption.
Should you use any other interface instead of the Bluetooth (e.g. SD card module), battery life will be greatly extended.
Note that you can always fit your BITalino with a higher capacity LiPo battery (e.g. 1Ah, 2Ah, ...) and adjust the battery life according to the requirements of your target application.