I suggest a mini UPS that can plug in the VIN power port (you would have to make you own barrel connector)

I have this one: https://www.amazon.com/gp/aw/d/B09JBYZ4KQ?psc=1&ref=ppx_pop_mob_b_asin_title

That I use for a lattepanda alpha (3A max). It lasts for 3 hours. I can plug / unplug wall power seamlessly.