We have to park our cars in a public area...and I'd think that someone would steal the solar panel eventually.
We leave our boat at a marina and take the boat out to the island. This is not us being close to the car in case of rain, etc either. We are 1.5miles out in Lake Huron and getting in may not be possible due to high waves and wind.

Because we don't have tablets, etc we won't be watching TV, and doing much downloading. I found last summer that coming here for 1 hr a day drained my battery in 1-2 days...depending on phone usage etc. 4G use on internet is very draining.

So I am thinking that doing the solar only this summer may be enough for us. Then as time passes, and if we do upgrade to a tablet someday, I'll need more power and then the batteries may be improved enough to risk a back up reserve one.
I was really shocked to see so many angry people. One highly rated brand Joos Orange, with a built in batt, had 3 negative reviews in May of 2014... and the reviews go back to 2010, with the company itself replacing cords, etc, on so many postings!
Seems even now the old defective units are still being sold on Amazon, and we just don't want that hassle in boonies. There are enough things to have to deal with up there! sigh.

So a fast solar panel may be it for this season after all!