A cursory look at the Skylla 24v manual shows that in addition to 7 pre-set voltage sets for specific battery models for various manufacturers, an 8th setting allows customised voltages fully adjustable via potentiometer, not via software.
Just last week I was looking at a newer product, the Victron MPPT solar charger, and the settings on it are adjustable via PC+USB connection, like Mastervolt, so I mistakenly assumed all Victron are adjustable via software! My bad.
The good news is, however, that no USB module would be necessary for this particular charger in order to get proper charging voltages for one's batteries.
SM2K Nº 350