I would not mix the lithium with the other batteries. I would replace ALL the house batteries with lithium. Otherwise you will be managing two different banks with different charging etc. Verify the charging system specs match the lithium battery before you purchase. Even with the increased usable capacity you may still need to increase capacity until you are comfortable withe the power duration. I would want capability of 48 to 72 hours minimum between charging even if you charge daily. This capability for if something goes wrong. You will know more what you need after a few nights off-grid.
