Pianotuna, I am persuaded by your first point! With solar, the batteries are discharged much more shallowly, both because some of the energy is provided directly by the solar and (more significantly) they are recharged every day, never even reaching the 50 percent state of charge at which I swap out my spare battery. And it is a well-established fact that batteries last longer when they are subject to shallow discharges, rather than deeper discharges.
I wonder if the extra battery life (more years of service) could help justify the cost of the solar. Instead of replacing my batteries every 5 years, maybe they would last ten, or whatever.
But I know someone who has had a battery die without warning -- me! In our early days of camping, we had one group 27. I checked the voltage religiously (i.e., I prayed I had enough juice). It died in the middle of the night. Our propane and carbon monoxide alarms went off as it died, just for fun. My wife has never forgotten that night.
The battery could not be revived in the morning.
Never again!
