Solar trickle charger needed

[_Deano]

I'm looking for a solar charger that i can connect to the battery on the car.
It's going to have to sit outside for a little while, and it may be in the same place for a number of weeks without being driven. The last thing i want is for the battery to die and then i encounter the electrical gremlins.

So far i've been looking around, most of the chargers, which can be placed on the rear shelf, have an output of about 1.5w to 2w. Only halfords offer one that can output 6w
http://www.halfords.com/motoring-travel/bulbs-wipe...

Given that the battery needs more than this to charge, is it possible to find a unit that output more?
Or do i just want a charger that will output enough wattage to keep the battery from dying?

[softtop]

I am also thinking about this as one possible option. Maybe it is because of volt drop, but is it possible to have the solar panel on the roof of the garage and then feed down into the car? Or would the cable just be too long.

[Impasse]

Maplin 4.8W clicky