Cigarette light is always hot with ignition on though.... So, even if you were just sitting listening to the radio, it would be a draw on the main battery..... That, and I would prefer something that didn't need any attention from me.

 

I think I will connect to one of my lighted mirrors on my sun visor, it only gets power with ignition turned on, that should be ok, what's your opinion?
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Those are very low-draw accessories..... not sure how much draw your charger is gonna have, granted, it shouldn't be very much, but, I would be worried about overloading that circuit.