Jaguar Solar Battery Charger

Winter is around the corner and I do not have a garage and wanted to keep my car batteries fully charged now that the cars are not used every day.  After much searching I found this Solar Panel at Harborfreight.com  The price was right and the specifications 1.5watts seemed just what I needed.  Also I leave it connected 24/7.
UPDATE 11/16/11

After my install I wanted to verify the charging capacity and other information about the solar charger.  I found that the panel has a diode to prevent back feed.  However, I needed to install a Regulator (you can also find it on the web for $15.00) to prevent the overcharging of the battery.  I asked if that was a problem when leaving it installed as you are driving and they told me that it was not but I needed to install a regulator when it is charging all the time to prevent the overcharging of the battery.

I installed one in my 2000 S-Type & 1999 XK8

To install I had to get a battery adapter to connect the solar panel to the battery.  The lighter in the car is switched with the key and would not charge when the car is not in use.

With this connector the positive connector has a fuse to protect the battery and the solar panel plug has a fuse to protect the system from and short circuits.

This test was done with the solar panel on the back seat and the doors closed.  I should also note that all the windows are tinted and at the time of the test the car was not in direct sunlight.