I havent read all the responses to your question, so I'm not sure if anyone has mentioned an inverter yet. As long as you're close to a vehicle it seems like a pretty simple choice to me and let's the Dji power source do what it's supposed to do.
Not sure if you can take the tablet back, i bought the Samsung Tab S6 and it works beautifully . Just plug in and it automatically goes to the App. They are a little pricey but well worth it