Flexible solar panel
We have one of those flexible solar panels, about 14 X 20 size. It is rated very low and cannot over-charge the battery. It does not loose power after dark. Those are the 2 things to watch for.We sleep on the boat, run some lights, stereo, VHF, charge our cell phones, depth, speed, etc. Not a lot of use but some. The solar panel tops off the battery and keeps it topped off. We leave it connected when we are gone for a week or so. Often we do not run the motor enough to re-charge the battery but the solar panel does it. It is not powerful enough to run anything directly off of. We use a cigarette lighter plug to hook up. There is a 12 ft cord, we move it around to catch the sun as needed. Easy to stow, non-breakable about $100.