My battery lasted about 5 hours, mostly in standby, with the wifi constantly broadcasting to my remote. We shot about 20 minutes of actual footage during that time before it died. I spent more time searching for fish that day than shooting movies so I'm sure I could capture hours of footage on one battery if I chose to. Nonetheless, I will bring my second battery aboard next time and keep it in a waterproof pouch.
We only caught a few fish this day and none were filmed. In future trips I plan to use my "selfie stick" mount to capture those amazing underwater fish fight scenes. This was my first go at the GoPro but I'm sure with time it will get better. I love the camera quality, am overly impressed with the suction mount and pretty pleased with the battery life.
Here's a link to the final 3 minute video we shot and edited.