A super capacitor lasts longer than a battery, and could handle short, but huge power demands better than a battery could. So they could help a little to increase battery life, but they cost considerably more- so probably not worth it to add them at the present time. Since many solar batteries are Li-ion, the best way to extend their life would be to avoid over discharge, and limit charge to maybe 80% of battery capacity. Like Tesla can do in their cars. And limit temperatures of course.