Northern Tool offers the Coleman 2.5-watt Amorphous Solar Panel Battery Maintainer, model no. 58016, for $9.99. Opt for in-store pickup to dodge the $6.49 shipping charge. That's $5 off list and tied with last month's mention as the lowest total price we could find. It includes a 12-volt DC plug and suction cups to mount it to a car dashboard for charging.