Here's a good web resource for how to charge a LiFePO4 cell.
https://www.powerstream.com/LLLF.htm
It looks like there are 4 cells in series. It's recommended to switch to "constant voltage" charging at 3.65V volts per cell. But to reach the ~13V of a car battery, I will never get into the "constant voltage" charging zone. So I guess I will slowly crank up the charging voltage until I hit whatever final voltage matches the lead-acid battery it's replacing. Unless one of you wise people advises otherwise
That's what intuition would have had me do, anyway.