I had the same happen on my 2018 Axion (manufactured sometimes in the last half of 2017) when I left the Lithium batteries on by mistake and they ran down. After reading the posts on this site, I removed the AGM battery from under the Axion. Took pretty much all day, had to jack up rear passenger side so I could crawl under and get access to the 8 bolts holding the battery up. Used a floor jack to slowly lower the battery until I could remove the cables. Battery looked pretty bad, 2 of the six caps were missing. Battery heavy, about 70 pounds. Hooked up a small 12 volt mower battery I had using jumper cables and started the underhood generator to start charging the Lithium batteries. Plugged in to shore power and everything worked, including the Solar charge. I plan to replace the AGM battery with a smaller (25 pound, 35AH) AGM battery. It appears that as long as the Lithium batteries are kept charged up, the system (inverter, solar, and UHG) work even with the AGM gone.