solar add on and batteries

I currently have 2 renogy 100 watt solar panels and a 20 amp charge controller and very happy with equipment and output. Plan on doing more boondocking this year so am going to install another 100 watt panel. I know my controller can handle up to 400 watts. I have 2 -100 amp deep cycle house batteries. My question is with the increased output am I better off keeping just the 2 batts or adding another house battery. Thanks
New York Newbie