Lithium Battery install ?

I haven't converted my trailer to Li yet but I've designed and installed Li battery systems for other applications. Li batteries have a very different charge profile from lead acid batteries. They can catch fire if overcharged. So in general you should not try to use equipment set up for charging lead acid batteries to charge Li batteries. Following that safety rule:

You already have a solar charge controller set up for Li battery charging?

That’s good for the solar but you can’t use a solar charge controller to charge from one battery to another. Solar modules are current sources, meaning that they will provide a limited amount of current (depending on how much sun they’re getting). They will provide current at a range of voltages, so the charge controller can decide what the output voltage limit will be for the battery type you’re using.

Batteries are the opposite, they provide a nearly unlimited amount of current at a fixed voltage. A solar charge controller is unable to change that voltage. If the battery you’re charging is at a lower voltage than the source battery the charge controller will try to supply all the current available, which is a lot, so it will either blow a fuse or burn up. If the battery being charged is at a higher voltage than the source battery the controller will supply no current at all.

Dc to dc converters can charge one battery from another by stepping the input voltage up or down to what you have set the output voltage to, while also limiting the current. But if you try do that youll wind up discharging your supply battery unless you shut off the dc dc converter to protect it.

Ok, I think maybe I understand but let me play it back. You want to replace the rpod House battery with lithium. You want to repurpose a solar charge controller you are presently using to charge a Li battery running a water pump. You are wanting to know if there are any issues if you place that charge controller between the existing battery cables and the new Li battery?

The main battery cables connect the battery to a buss which is in turn connected to the house 12v loads and to the WFCO charger via fuses in your panel. Since current needs to flow both ways in the battery cables that would not be a good place for the solar charge controller. If that controller is set up for the Li battery you can place it in the dedicated Zamp solar charge circuit feeding from the solar connection on the side of the trailer, if you have one,

If you want to charge your Li battery from an ac source I would not recommend using the wfco. It is set up for PbA batteries and is a poorly regulated charger so you could wind up with excessive voltage on the Li battery, which is very bad. Check the charging specs for your Li battery and get an appropriate charger.

You will also need to disable your tow vehicle charging circuit, or replace it with something else like a dc dc converter. Li batteries are actually easy to charge, you don’t need a fancy multistage charger like you do for PbA, but you must not overcharge them, ever.

The tow vehicle charging circuit doesn’t go through the wfco battery charger. That just runs from an ac source. When you connect your tv to the trailer you are making a direct connection between the two 12v systems. That works ok because they are both lead acid batteries and the resistance of the wire runs limits the current flowing between the two even if one battery is at a lower voltage than the other. The same direct connection won’t work so well with two different battery chemistries. There are dc dc converters available that can do the job correctly and safely but they aren’t cheap.

The electronics in your Li battery are there to balance the charge on the individual cells. Eventually Li cells become unevenly charged because they never get floated or equalized like they do in a PbA battery. That circuit won’t replace a proper charge controller although some of them do have a high voltage cutoff built in as a safety backup.

Wow....dont get me started....