Question

I have a solar panel on the roof of my motorhome but have also bought a portable one to increase the charging capacity. The one on the roof has its own regulator and coupled up to my 2 leisure batteries which are connected in parallel. This panel is only 68watts and really too small and that is why I have bought the portable one. My question is can I connect this one also to the leisure batteries and if so can it be connected to either battery, this panel has also got a regulator

Answer

Yes, this should be fine. Regulators normally include a diode to prevent any battery voltage being back fed to the panel. The extra panel can be connected to either of the positive and negative terminals.