You can’t run every model of GoPro with external power without an internal battery (i.e., pass-through power)-some models don’t have removable batteries. But you can with the Black models.
You can run the HERO9, HERO8 Black, HERO7 Black, and HERO6 Black with external power. The same goes with the HERO5 Black and HERO (2018). If you’re powering the camera from an external source via the USB-C cable, whether that’s a wall adapter, USB powerbrick, computer, or car adapter, you can remove the internal battery and run the camera via external power. The camera will continue to work normally. Doing this is known as providing pass-through power.
An advantage of leaving the internal battery in place is as a safety net in case the external power stops flowing. Without the internal battery, the moment that the AC power stops, the camera will turn off. It won’t turn back on automatically when the power source is restored. With the internal battery installed, it will switch over seamlessly.
But there are times when removing the battery might be a better option, especially for very long-term shooting such as time lapse and if you need to reduce the weight of the camera.
Water & Weather Considerations
An important consideration when doing this is that because it requires the USB port to be accessible, the camera will no longer be waterproof.
There are some accessories for the HERO9 Black to help with this. They don’t make the camera waterproof, as such-you wouldn’t want to submerge the camera-but they do maintain some water- and weather-resistance that makes them useful for outdoor above-the-water-surface shooting such as long-term time lapse.
GoPro has recently come out with a USB Pass-Through Door for the HERO9 Black that has a USB cable attached to the a replacement side door. You can then attach the cable (4.5 feet / 1.37 meters) to an external power source (it doesn’t protect the power source itself-that’s something you’ll need to handle separately).
And a third-party company called 3BR Powersports has a product called the X-PWR-H9 that provides much the same functionality, but it’s built into an aluminum cage mount. You can find them here.
External Power Indicator
Usually, when you connect external power you’ll get the charging battery indicator. Without any internal battery to charge, though, there’s a different icon on the front screen. It looks like this:
On the HERO5 Black, HERO (2018), and HERO6 Black, you get the same icon in the top right-hand corner of the back screen as well. On the HERO7 Black, you get a small “No Batt” message next to a red battery icon with a cross in it.