Automatically Shuts Off After A Few Minutes

I have the exact same problem. It’s a brand new gopro. It’s supposed to give me at least 4 to 5 hours record time, I know this can be shortened if I’m using very fine record etc. I do find that after turning it on, I go out for a cycle and when I come back after 1 hour 30 minutes cycle & discover that my gopro has switched itself off During play back I discover that the go-pro had stopped recording as soon I went around the corner from my house. I’m presuming this is when it switched itself off. The batter is fully charged. Unfortunately, I have no way of removing the battery as it’s built-in to the unit & is rechargeable via USB. This is extremely frustrating as it was expensive enough & given todays society, where most people, not all, but most anyway, are in competition with each other to see who can be most hazards to cyclists/pedestrians. I was hoping that the gopro on my cycle helmet would serve as a unbiased witness in the unfortunate even that I have an accident involving another cyclist, car, or, pedestrian. It’s only serving as a useless piece of weight on my head at the minute. I’ve done all I can in the menu settings thinking I had set something up that causing it to switch itself off, but, from what I can see, there’s no reason for it to do so while there’s still plenty of power in the batter. I’m on limited funds, so I cannot afford the swanky sleek cycle helmet cams. I can’t afford hundreds to fork out on it.