Connect multiple portable solar panels?

Probably best to buy a second panel with controller and run both sets of wires to the battery.

Otherwise you'll need to access the controller input wires to connect the second panel. Panels should be identical and the controller has to be spec'd for 2 panels and you may void any warranty.

Very common to connect panels in parallel, series or series parallel with 2 wires going to an appropiate controller.

Must also consider the max capabilities of the charge controller on the single panel. It may not be capable of handling more panels.

Not enough information for a good answer. Please send the specifications for the panel and the controller.

When I installed the solar panel on the truck camper, I thought far enough ahead to add a "connection hub". That way I can simply add an extra panel or two and plug it into the hub with out having to rewire the whole mess. But I did know that I would eventually add more panels and batteries. The system is sized to a specific size that I will eventually end up with.

Are the panels the same brand and specs?

If they are the same wattage but different voltage, that could cause issues as the higher voltage panel may waste energy trying to backfeed into the lower voltage panel.

It's best to have the controller close to the batteries. If possible remove the controller from the panel and install it close to the batteries. Do not place the controller in the same compartment as the batteries if they are flooded lead acid.

I have two 100 watt portable panels that I connect to one of my two portable Renogy solar controllers using a Jackery Y branch..They have the Y branch clones on Amazon...Not sure how your Renogy controller is connected but the two pannels connected, need to go into the input of your controller..The Y branch connects the two panels to make one inputto said controller..