The BT-02 is a rechargeable lithium-ion battery for the ZOOM Q4 and ZOOM Q4n Handy Video Recorders. Battery life is approximately three hours when shooting video at 720p/30fps, or two hours when shooting high-definition 1080/30fps video. You can use it as a spare battery for your Q4 or Q4n. WHAT'S INCLUDED Rechargeable battery for ZOOM Q4 + Q4n Handy Video Recorders