Even if you can manage to find li-ion cheaper, you would need to build a pack of 6+ 18650 cells for comparative capacity. A single Pb is much simpler. Bam, $18, done, a single unit, 80Wh ready to go, super simple to charge too.
It's not like the size or weight matters to him, and it seems his panel is big enough to avoid deep cycling it too often.
It's not like the size or weight matters to him, and it seems his panel is big enough to avoid deep cycling it too often.