Signature solar bi-facial panels have PV wafers on each side, hence one female and one male connector on the back side of each panel. I was mistaken about it being two female connectors. Here are connector sets that I see on-line.
Also I tried ordering two SOK 12.8V 100Ah Lithium Iron Phosphate Batteries from Powermaster USA but they are limiting orders to only one. I can't seem to contact them but that probably wouldn't help anyway. Can anyone out there help?
The image, if connected, shows parallel. For series, put the Y cables away. Connect one panel's red to the other panel's black. The red from one panel and the black from the other panel (that are not connected) are your series output. If you are old enough to remember D cell flashlights, the batteries stacked end to end, negative bottom, sitting on positive top of the other battery. Any series power source connects the same way. Voltages add up, so if your panels are 18v open circuit, you should measure about 36v in the sun open circuit, if you have them connected in series.