I have one of those units, a Yeti 3000X, courtesy of SDG&E, our local power company. It's a battery, an inverter and a DC-DC converter packaged together, with a small external charger. Also has Bluetooth. Sells at Costco for $3500.
So, I got it because it's free and had a Li battery inside. Then I found out that the battery is 10.3 volts ( 3 cells at 3.6 VDC?), so it's not good fit for the boat. The 3000 model puts out 3000 WATT-hrs at 10.3 VDC And with the supplied charger, it takes 13 hrs to charge from the wall. The solar panels which come with it take 24 hours to recharge it. It will run the house refrigerator for about 22 hrs, which is a plus.
So, since I can't pull the battery out and use it, and the inverter is designed to operate with an input of 10.3 VDC and it takes a long time to charge, it's useless. It sits in the garage taking up space; anyone who wants it can stop by and pick it up, free. It's useless to me.
Boris