That would work just fine
At present the Odyssey and the Auxiliary are in parallel until I can seperate them with said device or other.
Am I at risk of damaging the odessey in the interm?
yes, anytime you have 2 different batteries joined together like that there is risk of damaging one, the other, or both, this is why we always recommend to people to replace both batteries together, with identical ones, the weaker battery has a tendency to draw down the stronger one.
As for the isolation, there's another thing to think about, at what point do you want your batteries to be linked? Obviously when the engine is running you want everything linked together to charge both, but what about starting? imagine the following:
- you've been camping and using the auxiliary battery a lot, you've drained it pretty far down
- it's cold out and is going to be a relatively tough start
The last thing you want is to connect your dead auxiliary battery to the good starting battery at the same time as trying to crank over the engine, you'd be wasting a lot of badly needed electricity being dumped in to that weak battery.
now on the flip side, imagine a case where the main battery has been run down, now obviously having the 2 linked together would be a plus as it can give that extra oomph to get the vehicle going when the main battery is dead.
My recommendation is to hook up the isolator such that it joins the batteries only after the vehicle is actually running (take a feed from the oil pressure sensor, or the alternator) and carry a 6" jumper cable. this way you can always boost your vehicle from the other battery, but by default you don't draw down your strong starting battery with a week auxiliary battery until the engine is actually running to charge them both.