For the 12v battery, you can use a UPS 9ah battery or small LFP 12v 6ah battery. Both are very lightweight, very cheap ($25 for LeadAcid, $35 for LFP), and would more than satisfy the demand from the charger. Otherwise, a buck converter directly to the charger should work.
This guide covers everything you need to know about solar costs, including average prices per watt, system size estimates, incentives, regional differences, and payback timelines. As of 2025, the average cost to install solar panels in California is around $2.