Controlled current when charging

Does anyone have a solution to charge the battery with a lower current? I have the 2.5 system with the 2.6kW battery and when I go camping, wanted to charge the battery with my 12V power outlet.

I do it with a 2kw 12vdc to 120vac inverter in my RV but it’s not very efficient, there are 12vdc to 100vdc converters available that would be more efficient, someone posted their setup on the list earlier.