Agreed, my answer was just being a goof.

I would say that not only is solar the most viable, but probably the only option. My sons Jetta came with a solar panel that has suction cups on it and a cord to go in the accessory port. Won't work for us because those ports are dead when the car is off so it would have to be hard wired.

 

I just velcroed my panel to the back shelf at the rear window and ran the wires to the boost posts in the engine bay. Don't wire directly to the battery in the trunk, as that will screw up the IBS.

 

Solar battery tender idea looks interesting, 2 questions

1. which one should I buy 5/10 or 15W?

2. Can I use cigarette adapter to change my 2008 BMW 528i?

Thank you all

 

The bigger the better in my opinion. As far as using the cigarette lighter, I doubt it. My 2007 kills power to the aux ports when the ignition is off and I would guess there is no reason for the 2008 to be different.

 

5 watts is plenty, otherwise you run the risk of overcharging with unregulated 10/15 watt units. Also, use the terminals in the engine compartment - the cigarette etc, outlets are not live when the car is shut-down.

 

Most likely 5W or if higher then a converter will have to be added to this.