Both.
4x 12V batteries in series is 48V. But for lithium, we recommend a 48V battery, so one BMS controls all cells.
PV panels are nominally called 12V, 24V, 36V, but vary considerably with load. Typically 20V, 40V, 65V, 80V or so open-circuit.
You connect them in series so Vmp voltage is enough above max battery charging voltage for the SCC to work. But Voc never exceeds max allowed, even in cold weather. Typically 100V, 145V, 150V, 200V, 250V, 450V, 600V, 1000V.
Higher voltage charge controllers cost a premium, more $$ for fewer watts. Some panel voltages and current just don't fit some SCC well. So entire system design should be optimized before anything is purchased.