There’s automotive plugs which use more or less standard spade connectors which you can wire yourself and they can easily achieve 10A and things like relay sockets can manage 40A or more. JAE is one of the brands manufacturing all kinds of connectors, with and without panel connectors, but there’s a ton of manufacturers around. I suppose on marine stuff you can find connectors like that too.

But if it’s for a LED strip and you don’t need to constantly move them around, I’d suggest using a dirt cheap spade connectors with color coding (reverse male/female connectors on the live one so it’s physically impossible to connect led strip in reverse polarity). Or even cheaper, use screw terminals and be extra careful when wiring the strip in.

And for the dupont-style connector commonly seen on LED strips, 10A feels like quite optimistic value. Obviously a LED strip can pull 10A and many times that, but quickly googled ballpark estimation for 2,5m 10A led strip calls for 2,5mm² wiring all the way trough and your cheap flexible LED PCB from amazon/ebay is pretty far from that. But that depends heavily on what you actually have and if you’ve measured 6A then it’s pretty reasonable to have the rest of the setup to manage 10A.

12V 200A relays are pretty easy to find (I wouldn’t get one from alibaba tho), but that much current requires quite beefy wiring as well. Personally I’d review options to place auxiliary batteries in parallel since that would simplify wiring and the whole system a bit, but as I don’t know how your camper is built it can be tricky or you need to sacrifice storage space somewhere.

And as you’re placing a battery at the same space where people stay be careful with hydrogen. Charging lead acid battery produces hydrogen and in the worst case scenario, specially if you have a gas stove be dangerous if not lethal.

So you’ll have total of 3 batteries at the car? One for engine, existing utility battery and now you’re planning to install another utility battery, right? That should work. I don’t know how much current you’re pulling from the battery, so it’s difficult to recommend anything. Common bosh switching relay is something you can find from pretty much every car part store for ~5€, but I think they’re rated only up to 40A and I wouldn’t push them to the limit. Check your inverter datasheet how much current it can draw and preferably get a relay which can do double the maximum rating for longevity and stability.

Get a switching relay or one normally closed and another normally open one. That way there’s no paraller connection at all. Connecting two batteries together with different voltage levels causes a huge current spike, think jump starting a car and how thick those cables are. Arcing will happen on the relay contacts no matter how you switch it if there’s load connected.

And since you’re not talking about a trailer, is one of the batteries for the car itself? Since if you’re planning to use the secondary battery as a car battery too you need very heavy wiring to give starter enough amps to run plus running that over a relay is a whole another beast to manage since starter motor can pull hundreds of amps momentarily.

You want to put the batteries in parallel, so you’ll have double the capacity. Installing them in a series would increase voltage and most likely damage something (mixing 12V systems with 24V battery pack doesn’t really work). Increasing capacity with another battery can cause strain on charger components, so make sure they’re beefy enough or at least have proper protection against overcurrent.

People are correct that you should use the same capacity batteries, preferably the same make/model and age. Mixing batteries can cause problems where one battery drains faster and other(s) start to charge the lower level one so you’ll have less useful amp-hours and that degrades batteries faster.

Switching batteries with a relay or a switch is possible, but you need quite big and good quality relays/contactors for that as current can be pretty high which can cause arcing and even weld contacts together eventually. With proper parts it’s a safe way of doing it, but personally I’d just get two batteries in parallel since there’s fewer components to malfunction and adding complexity with arduino+contactor doesn’t save that much money, specially if you place any value for your time (which of course isn’t necessary, tinkering itself is often worth the time spent).

But the end goal would be to only use that to build the network, connecting modes together through $VARIOUS_MEANS, and implement the Yggdrasil code right at the network card level.

So, eventually it might be a (new) internet with encryption (and blackjack+hookers?). I already can connect my house trough neighbours connection (with limitations like NAT of course), but once ipv6 is available everywhere I don’t immediately see if Yggdrasil offers anything else than protocol level encryption. Current internet is a mesh network after all, just built a bit differently and more controlled manner.

Interesting concept anyways, maybe it’ll catch up some day.

In short: No.

Assuming that I understood correctly with a quick reading that’s creating a whole another network on top of existing internet and requires raw bandwidth to function at all.

Various mesh-networks have been around for quite a long time to solve the ‘last mile’ issue on poor areas. That requires pretty dense population to actually work, but at least couple of years ago there’s been some moderately successful projects. I haven’t followed those in years, so I don’t know what’s the current status and that’s very different from what Yggdrasil is doing.