Charging lithium conversion

I am converting a trailer from lead acid to lithium power.

Others can comment on my plan.

My built in charger does not support lithium. It does support operation without a battery. I will not install a lead acid battery at all in the system.

I plan to add a separate circuit with a lithium charger and battery. The only connection between the 2 circuits will be with a NC relay triggered on the output of the existing charger with a diode connecting to all the loads.

With AC connected:

This will create completely separate systems This set up should allow 100% of lithium charger to go directly to the lithium battery. This will allow 100% of the convertor to go to house loads.

With AC disconnected:

AC power is disconnected, 100% of the power is provided by the lithium battery.

My goal is to use as much of the charge capability with minimal cost and time for a quick upgrade. And I assumed this would be quicker ton install than replacing the complete power wfco-8735p with the drop in replacement that supports lithium.