Correct, you can connect an expansion battery to the AC180 via the DC Input Port. This is the the same port you would connect solar to. This port allows the AC180 to be charged at a maximum of 500W.
For the AC180, the expansion battery must be used in Power Bank Mode.
The expansion battery will charge the AC180 via the port and that it is it.
You will need to purchase the appropriate cable for the expansion battery you are looking to use.
The AC180 and the expansion battery are not “linked” as other Bluetti power stations are.
Thanks. I would then imagine the expansion battery has to charged by other means. Might be wise for me to get a model which is expandable and connected fully.