Lithium battery installation

If you already have a battery cut-off switch, run the same connection, most likely positive, to it. The negative cable can be shorter and just go directly to the frame. If you look at your existing connections, they will be the same except you won't have a jumper between two batteries since there will only be one battery.

It sounds like you are all set converter wise. That makes it a lot simpler. The other consideration though is whether you want to take the trouble to install a DC to DC converter so your tow vehicle can charge the battery while you are on the road. If you are not going to be going any great distance, it might be optional. In our case, when we travel across the country, I need to be able to have the tow vehicle charge the battery.

Ouch! I hope your recovery goes well. At this stage, getting a small inverter generator to charge the batteries you have is likely a better option than trying to upgrade to an LiFePO4 battery.

Quick answer on the old charger is no, it wouldn't be adequate. It was made for lead-acid batteries, and most likely flooded lead-acid batteries. Unless it has settings for AGM, Gel, or other types, it is meant for flooded lead-acid and possibly sealed lead-acid batteries only. Only if it has a specific setting for LiFePO4 batteries would it be suitable. The charging profiles are too different. For example, LiFePO4 batteries do not use a float charge.