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I would love to help you with this.
I think that you shouldn't have problems using the power socket, because the Edison is never going to need more than 15 A, so answering your question, yes it is a safe source.
Having said that, the only recommendation that I can give you is to make sure that the Car Adapter Plug provides enough current to power the Edison, the Edison is not going to draw more than 500 mA.
I hope you find this helpful, and don't doubt to contact us when you have questions.
Have a nice day.
I don't think there would be an issue with hooking up the edison to the car battery. The edison will draw the amperage needed on it's own, but it will be far and away less than .5 amps, so you shouldn't run into issues.
(Disclaimer, I have not done this.)
Thanks for the response. I will look for an Electricity 101 course to make me more self sufficient