Based on my research, using a cigarette lighter adapter to charge an Air is not recommended. The car's circuit breakers might trip or the adapter itself would overheat.
I did read about DC to AC to DC inverters.
What about a Mophie? It probably wouldn't charge the battery, but would maintain the charge.
What does Apple recommend?
Personally, I don't trust the lighter adapters for charging even iDevices - my wife's phone blew a few fuses on my previous car - I bought her a small battery pack that can charge her new iPhone or iPad Mini at least twice while in the car. SO, that would not be an option for me.
But, there are more powerful battery packs that can charge a laptop - keep in mind the wattage needed (my MBPro has a 60 W charger) - there was a previous thread from a poster asking about the
BatteryBox (shown below) that would serve your needs - not cheap (believe about $200) - assume that you've been googling similar products?
As to Apple's recommendation, this forum is not supported by Apple, so unless you join one w/ Apple technicians responding or visit an Apple store to ask your question, I cannot address your query - maybe others can? Let us know what you decide - good luck in your selection. Dave
P.S. I have a battery pack for my iPad, but have not used one w/ my laptop, so the above is not a personal recommendation for the product mentioned.
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