I have a setup consisting of 2 x 330Wp panels connected to a blue solar 100/50 controller to charge 2 x 190Ah 12 batteries. This setup is for an off-grid cabin that will not get use during many months (6-9). During these months, the 330Wp panels will be disconnected and stored. The question is: Can I use a small 20W (21.5Voc) panel to maintain the batteries topped during these 8-9 months via the MPPT charger?