First question: is the converter lithium-compatible?
A converter made for flooded or AGM batteries may still put out voltage, but it may not charge LiFePO4 batteries fully. Some owners see the battery climb partway and stop. Others see the converter fan run but the battery monitor barely moves.
Check voltage at three places
- Measure at the converter output.
- Measure at the battery terminals.
- Measure while the battery is actually accepting current, if you have a battery monitor or clamp meter.
If voltage is good at the converter but lower at the battery, you are chasing wiring, fuses, disconnects or voltage drop rather than a charger setting.
Lithium batteries can go to sleep
Many lithium batteries protect themselves with a battery management system. A deeply discharged battery may appear dead until it is awakened with the correct charger or reset procedure. Follow the battery maker's instructions here; do not jump random terminals just because an internet comment said it worked.
Cold charging matters
Standard LiFePO4 batteries should not be charged below their specified temperature unless they have built-in low-temperature protection or heaters. If the battery is cold and refuses charge, that may be protection doing its job.
Do not forget the old RV parts
Check reverse-polarity fuses, main battery fuses, loose frame grounds and battery disconnect relays. A lithium battery will not fix a corroded cable end or a half-burned fuse holder.