There have been lots of questions on whether or not the factory WFCO 8735 converter that doesn’t “support” lithium batteries is capable of charging them sufficiently.
I have a 2021 Geo Pro with a 100ah Screampower Lithium Battery and the WFCO 8735 non lithium converter. Prior to having a battery shunt my limited testing showed the converter is capable of charging lithium batteries, but not to 100% and usually very slowly. After getting my Victron Smart Shunt this past weekend I can confirm the behavior I saw earlier.
Before I get very long winded, the WFCO 8735 is completely capable of charging a lithium battery up to at least 90% and sometimes 100% but the key is that the battery has to be at an extremely low state of charge to do so.
After drawing down my battery to 13.0v I plugged the trailer in to shore power. I observed a 17amp spike of current that progressively went down and down but was mostly around 4-6 amps. Charging at a painfully slow speed. After 16.5 hours The battery was at 96% and zero current going through the battery. The previous 3.5 hours I wasn’t able to check (I was sleeping) but the converter likely charged the battery up to 100% and then the voltage started to drift down as the converter likes to stay right around 13.5v. So in this test we have the converter basically charging the battery up 100%.
In order to make sure it wasn’t a false recharge reading I put a bunch of draw from some small space heaters I have until I kept hitting the inverter cut off (10.5v, my battery will actually function down as low as 10.1v) I was able to measure 100ah of energy drawn, indicating I did in fact get a full charge.
Next was to plug in to shore power from a very low voltage (11.0v) and observe the charging current and speed. As soon as I plugged in to shore power the converter charge current spiked to 33amps, and gradually dropped over 3.5 hours to a low point of 17 amps before turning off because the battery was fully charged. After 30 minutes of being nearly fully charged the state of charge started to drop down (just like it did when I started a recharge from 13v indicating the converter does draw the battery down when not actively charging)
So it took almost 14 hours to charge my lithium battery from a starting voltage of 13.0v, or 3.5 hours from a starting voltage of 11.0v using the factory non lithium WFCO 8735 converter. Once fully charged though if the converter is left on the battery does get drawn down
The method of charging, high current and voltage slowly rising with the converter charging is the exact same behavior that my 10amp lithium specific charger that came with my battery came with.
So if someone did not want to swap out their converter to a lithium specific one there are a few “issues” to deal with
1. You need to turn the converter off from charging once it decides its done charging, which is between 90-100% soc.
2. You need to have your battery at a very low state of charge. In my case 11.0v works (My BMS cuts off at 10v)
3. Not an issue but if you have the Go Power solar set to LFP mode it will finish off the charge for you.