My group 24 battery would only last about 3 days, just using lights, water pump, and recharge of the occasional device. It isn't good for a battery's life to be drawn below 50%, either. So last summer I spent less than $150 on a 75W solar panel and Morningstar SG-4 controller. I rigged it up to plug into my trailer's pigtail (the one that goes to the tow vehicle) and set it out in the sun. It tops off my battery every day, problem solved and I can boondock as long as the water holds out.
I sold the trailer yesterday, but you can bet I kept the panel for my next trailer!
Mike G.
Liberty is meaningless where the right to utter one's thoughts and opinions has ceased to exist. That, of all rights, is the dread of tyrants. --Frederick Douglass
photo: Yosemite Valley view from Taft Point