Manual control and monitoring while charging Lead Acid / AGM batteries. Also used to manually charge Lithium by pressing the Button Monthly or when charge is needed.
So this pendant just shows what mode the charger is in (Boost, Normal, or storage mode) and lets you Manually select the mode.
However, you question was "to allow it to properly charge Lithium batteries". I don't believe that even PD Lithium series chargers properly charge LiFePO4 (LFP) batteries. Until last fall (2021) their Lithium series chargers were simply current-limited 14.6V power supplies (not really chargers). They would apply 14.6V to the battery forever. This would stress the LFP battery cells and certainly severely reduce its life. Then in the Fall of 2021, they came out with a "2-stage" Lithium charger what would reduce the voltage to a "Float charge" of 13.6V.... so that's an improvement.
However reading their literature, when the charger is first plugged in, it will goto Boost (aka Bulk) charge for a minimum of 1 hour. The issue I have with that is my battery may already be charged (maybe it was a brown-out, or someone tripped a breaker) and sitting at 14.6V (Max charge voltage) for an hour just because the charger powered up is a lot of unnecessary stress on the cells.
Unlike Lead-Acid, LFP batteries do not need to be fully charged all the time. They are actually happier if they live in the 10-90% State of Charge. So pushing the charge voltage to the Max is not really needed. I run mine at 14.2V which gives me 95+% and float at 13.5V.
LFP like to be stored with about 50% state of charge, so don't leave it charging all winter. Run it down to 50-60%, then disconnect it and bring it into the house where it can't freeze and leave it be.
Trouble is, I haven't found a "programmable" converter/charger that I could recommend. Closest I have found is a Samlex EVO series which is an Inverter/Charger/Transfer switch unit. It's completely programmable to handle all popular battery chemistries and charging parameters. But being an all-in-one unit, it is more expensive and overkill for most people. The Victron units fall into the same category.
Best is to do some reading on the subject. LFP are actually not as finicky as Lead-Acid.