I record with Nikon D3500 always on my PC Desktop and I want it to be ON for 7-8 hours. But the battery life is too short. How can I connect to a power or something to keep ON all the time ?
Nikon produces a battery adapter for the EN-EL14a battery in your camera. With this you can power the camera directly with a wallplug. This can be found for example here on amazon.com
But keep in mind: the d3500 is not build to film over such a long time. so the sensor can get heat problems, damages and can die faster.