TAG 320 lithium battery conversion

eddycurrents

Hi all.  First time user here.

My wife says that there are numerous online accounts of a "smart" alternator's output being used via pin 7 of the trailer connector to directly charge the camper's two paralleled lithium batteries with no issues, despite the fact that the tow vehicle's battery (in this case a 2023 Maverick) is of the lead-acid type. 

Would this mean that the alternator's built-in voltage and current regulation is biased for whichever battery type wouldn't be harmed by the other one's charging voltage/current being used? Or does the pin 7 connection originate from a separate smart regulator circuit, independent of the one that charges the truck battery?

Otherwise, could these stories simply mean that the users are getting away with a risky setup, and there really should be an Li charging adapter (the so-called DC-DC converter?) between the truck's 12V+ supply and the trailer?

Thanks for any and all input.

-e

Grumpy_G

Way to open a can of worms ... There is only one voltage regulator and it is designed/computer controlled for the type of battery in the tow vehicle. LiFePo batteries need a higher charging voltage so they won't be fully charged. They also have a higher resting voltage when fully charged (e.g. via solar or a dedicated charger at home) so they can backfeed into the tow vehicle. That is not an issue as modern vehicles can ramp up voltage to over 14.5V so the electronics are designed with that in mind. 
DC-DC converters do solve the charging issue but also drastically increase the current draw from the tow vehicle which typically blows the trailer power fuse. That's why people end up installing dedicated trailer charging wiring in the tow vehicle.