There are compromises with everything and the fact you need to bypass it is concerning to me. You say you're trying to save 20Ah by disconnecting some of your loads, but your not disconnecting your biggest load I don't get the logic. I'd run that just for the inverter and nothing else personally.
A lithium jump starter pack that doubles as a portable USB charger are less than $100. I know what I'd prefer. One less thing to go wrong (when bypassing even) and one that is multi-use. But hey I consider more than most people too.
I do like Victron gear though. My house is offgrid with lithium batteries and Victron equipment, so I'm bias too.
You need to think in terms of AH rather then just A
Yes I have a 2000w inverter, no it is not consuming 2000w constantly
I boil the jug, 185 amps for 2 minutes this uses 6.1 AH
Remember the rest of the car "bypasses" the load disconnect as well so stereo and parkers ect will draw the battery even after load discon operates.
How is this any worse then a traditional multi system setup?
Do u wire up your stereo to your second battery? Ok so some do..
Well u can all so do that with the load discon.
It's up to you what you want to allocate as main and aux loads and how you use them.
My inverter does small loads like charging phones or big ones like boiling the jug.
Small loads need quite a while to get the BMS to open circuit, maybe a few days.
Big loads, you are with the car as they are happening so its fine provided u dont try to boil the jug with less then 20ah remaining (battery protect will indicate this)
Even if you did, you would have 14 ish AH left to start the car which is plenty with these lithiums.
Another advantage of single system setup is the solar charges all, not prioritising one then the other like a traditional lead acid with say a sbi12d would do, and depending on the energy supply and demand perhaps never getting to charge the main battery again, which leaves you not being able to start the car because you were playing the stereo for to long or doing something equivelant to this.
It would help to draw it out but also consider a rational theory of operation
You are not going to run your 12/240v bd series comp fridge off 240v in your car just because you have an inverter and you can, you would likely wire it in 12 so you arent converting the power twice for no reason. Its not efficient.
And as said above, im sure my inverter can be programmed to cut off at a voltage point as well if i want so it is its own load disconnect
I just haven't been bothered to try because I haven't had any real issues using it the way i have been