Just a note on wiring batteries in general: it is much safer and more reliable to hardwire a parking battery directly to your car’s main battery with 12g wire and a heavy duty 40A time delay relay than to draw that much power from your fuse box. Some of these parking batteries draw FAR more power than they claim to. This can cause problems for your fusebox, especially in newer cars (any car with a screen instead of knob and dials on the dash) with sophisticated battery management systems and smart fuse boxes that monitor power draw.
Your parking battery can be installed in the glove box, in the trunk, or under the passenger seat. If your wires to the dashcam are more than about 10ft or so, be sure to use heavier wire (20g is fine, 18g is better) so you don’t lose too much voltage on the way to the camera.
