I currently have a DC-DC boost converter on a split charge system going into a Lead Acid leisure battery (LB).
It's a cheap 400W module but it has CV & CA limiters so I can set it to 14.4 volts and 10 amps and it will top up my LB when I'm driving. Main reason is to maximize the top up charge from short journeys.

So I'm now thinking I might like to fit a LiFePO4 battery instead of the lead acid LB, and from what I have read the charging system I have now will work fine apart from one aspect - over charging through extended float charge.

What I think I need is something like a smart relay module on the DC-DC converter output that monitors the current and if it drops below 2 amps it opens the circuit and latches it until the vehicle power is cycled.

Does anything like this exist or so I'd need to make something?

 

Something like this, wired across an appropriate sense resistor, might work for you.

 

Something like this, wired across an appropriate sense resistor, might work for you.

Yes, though I have a feeling that one won't be sensitive enough.
1v at 10 amps is 10 watts across a 0.1 ohm resistor, which will get warm but not too hot if it was a 50 watt alloy resistor, especially if I use the vehicles body as a heat sink.
So as you've suggested, that an a voltage sensing switch or relay could do the rest.

 

Alternatively, you could use a Hall effect current sensor to reduce power consumption. You would have to convert the output to a voltage, or, if you interested in doing it, you could use a very simple MCU to deal with the cutoff.