If I had 2 AC180’s, could I plug the one I was using into an AC port on unit #2 thus using both 1,150 WH = 2,300 WH?
They can be charged with each other. But the total capacity does not increase.
If you have the first 180 100% charged, the second 180 can be connected to the AC input of the first. Unit # 2 will then have its AC output passed through unit #1 and when unit #2 has exhausted its battery, Unit #1 will take over and discharge. So yes, it works great.