Isn’t the expansion port an input and an output? Seems like it should be listed as an input, with specs. Before buying an expansion battery I’d like to know what input the expansion batteries can handle when connected to my AC200MAX. Is it 200W, 500W, 700W, 900W? For example, I have 800W coming in to my AC200MAX. If I attach a B230 will the input get divided evenly as 400W/400W? If the main battery is full, will the B230 use all 800W?

I think the above thread answers your question.

Thr B300 battery has 16 lithium iron phosphate (LFP) cells in series. Each cell is rated at a 3.2 VDC average , so the total voltage is an average of 51.2 VDC. The average cell current rating is 60 Ah so the total B300 battery power rating is 51.2 x 60 = 3072 Watt-hour (3072 Wh). The P090A cable has 90 A rated DC contacts and in theory the maximum battery current may run up to 80 A or over 4 kW but each controller has internal circuitry limits. The AC300 limits that power down to 3000 watts or 3 kW, so the battery current output is about 60 A. This is converted to 25 A at the 120 VAC output.