ECO-WORTHY US via Amazon also has ECO-WORTHY 5W Solar Car Battery Charger Maintainer for $16.99. Shipping is free w/ Prime or on $35+ orders.

Thanks to Slickdeals Moderator Wiznaz for finding this deal.

Features:

• Suitable for keeping vehicles/boat battery charged during the weeks unused. No need to disconnect the battery or have someone start the vehicle periodically. The indicator light on the back can observe the charging state. And it’s waterproof, you can safely use it outdoors(After experimental test).
• The 10w monocrystalline solar panel uses trickle charging to charge the battery without causing overcharging. Built-in blocking diode prevents reverse charging without extra maintenance at night. Works even on cloudy days. As frosted surface, the panel doesn’t need film protection anymore.
• Equipped with SAE cable, just plug the cigarette lighter into the port or connect the battery terminal posts with the alligator clip, and the connection can be completed within 3 minutes! Suitable for car, truck, boat, lawn mower, motorcycles, trailer, dump trailer, tractor, RV, van, camper, ATV, utility vehicle Battery etc.