To connect the two batteries in parallel you will have to connect the negative terminal of the first battery to the negative terminal of the second battery and vice versa as shown in fig.
How to parrell wire solar panels.
To wire two or more solar panels and batteries in parallel simply connect the positive terminal of solar panel or battery to the positive terminal of solar panel or battery and vise versa respectively as shown in the fig below.
The positive wires are connected to a positive connector within a combiner box and the negative wires are connected to the negative connector.
Rather than connecting the positive terminal of one panel to the negative terminal of the next when stringing in parallel the positive terminals of all the panels on the string are connected to one wire and the negative terminals are all connected to another wire.
The video will go over the basic installation and can apply directl.
Stringing solar panels in parallel shown in the right side of the diagram above is a bit more complicated.
When solar panels are wired in parallel the positive terminal from one panel is connected to the positive terminal of another panel and the negative terminals of the two panels are connected together.