question

Don’t forget that you also need to protect your alternator. Here is a video explaining why:

https://youtu.be/jgoIocPgOug

Just use a DC2DC charger hanging from the crank battery to the lithium bank.. Victron make a few different ones.. other make some combined DC2DC chargers with MPPT controllers built in. The crank when full wont take any charge.. and passes the alternator charge to the house.. I'm running a pair of 50a DC2DC MPPT chargers in parallel for 100a charge from the engines.. as they run from the crank batteries the wiring is pretty simple, with the exception I float the cranks from shore power so have a relay on the feed line to the dc2dc chargers ignition controlled.. so cut off the cranks from the chargers when the engine isnt running..

Example of my wiring below

Thanks for the suggestions - I was avoiding using a DC2DC charger. I have a 180A alternator and going to use the REC A BMS controlling the Wakespeed WS500, with an alternator temp probe attached, which then controls the output of the alternator for optimum lithium charge performance. Hence the DC2DC chargers are an unnecessary expense if I can get away with it.

I would have thought that the lithium battery charge settings in the WS500 voltage wise are less than the lead acid battery requirements . ie a LA battery usually needs bulk charge for 4- 8 hrs before its full , where a lifePo4 usually is set to 1hr or less. and the lifepo4s voltage is usually less than the LA battery's requirement 14.4 to 14.8 anyway, so as long as the lifepo4 setting is less you should never overcharge your lead LA starter battery.

yes over charge amps might be a issue but as they are starter batteries they usually would never be that flate for you to worry about.