What if there were a way you could get all the switched power you could want, to feed your cam battery as fast as it can take a charge, to power all your other devices and chargers, etc?
Let’s say you have a switched fuse somewhere inside the cabin or under the hood. Tap that and run a small wire (like 18AWG, it doesn’t take much current) to trigger a relay whose power is fed directly from the battery through the firewall. Switched fuse is under the hood? Mount the relay under the hood somewhere, too. Fuse is inside? Even easier.
For work under the hood, if you’ve got ring terminals with heat shrink, use those to help prevent any moisture intrusion and corrosion of the wiring. Use Posi-Locks rather than butt connectors if you’re mounting a rely there, using a relay harness (preferred), or if attaching directly to the relay leads then see about grabbing some spade connectors with heat shrink tubing. If you don’t have any already handy and don’t feel like buying some, slide on your own marine grade heat shrink tubing on all connections under the hood. Always good to have a variety pack of decent heat shrink around. Here’s a great collection for $10...
https://www.amazon.com/gp/B071H5XC7C
To do so, get a simple normally open relay of sufficient amperage capacity. 30A is common and way plenty. It doesn’t hurt to be able to handle more than you’ll draw. Use a Posi-Tap or add-a-circuit to use that switched fuse to trigger the relay. Run power to the relay directly from the positive terminal of the battery, with an in-line fuse near the battery connection. Ground to any nearby chassis bolt (not the negative terminal of the battery), ideally one that appears to be acting as a factory ground point already. Now you’ve got all the switched power you could want.
Here’s a waterproof relay with harness that would work well for you. It’s $10. Or get a 5-pack for $25.
https://www.amazon.com/gp/B074QV54V1
And here’s a 5-pack of 12AWG water resistant fuse holders to use as the battery end of the connection. Again, use marine grade heat shrink tubing to protect all connections and terminals other than Posi-Lock brand stuff.
https://www.amazon.com/gp/B0002KR88A
Run a feed wire through the firewall (no need for a ground wire) to wherever you want it to end up. Then use anything from a simple power bus (with each fed lead having its own in-line fuse) to a fancy RigRunner style fuse block to supply power to all the things, either way grounded to a an appropriate chassis screw/bolt. Or just use some Posi-Taps sunk into that one feed wire, I guess
What size wire to use depends on how much current capacity you think you might want, and to some extent how long that wire is, though in this application it should end up being fairly short anyway, certainly less than 10 feet. Always oversize at least a little. Consider 14AWG the minimum. Here’s some decent 12AWG wire that should be sufficient (unzip the black wire and use it separately)...
https://www.amazon.com/gp/B01ABOPMEI