GoPro USB Battery Chart
Simple chart to show how much the USB charger extends video time
The GoPro Hero 9 battery is much larger than previous versions of the GoPro. One nice difference between this version and the GoPro Silver 7 is that you can replace the battery.
In my tests, I have found that the internal battery in the GoPro Hero 9 lasts just more than 2 hours when recording Time-Lapse mode in 4k. It's closer to 2-hours in extremely cold conditions.
Taking Longer Videos
One way to take longer videos is to use a USB power source. This can be a wall outlet or a USB portable charger.
Yes, the GoPro will record when connected to a USB portable charger!
Chart showing the amount of GoPro Hours you get for various USB Chargers.
I have a USB hand warmer that has a 7,800mAh power charger. In my test, I have found that this makes recording time to 6 hours! You get 4-hours of USB power charge time and then the 2-hours of GoPro battery time.
This means if I get a 10,000mAh charger that my total charge time should get to 7.3 hours. (5.1 hours via USB and 2.2 hours with the GoPro battery)
I have a smaller 5,200mAh and according to my calculations that should give me 4.7 hours of total recording time.