Am I correct that currently, according theBluettipower.com web site, that the only expansion battery option for the AC200L is the B300K?
The AC200L user manual shows B210. B230, B300 as usable.
Here in Australia the B210 & B300K are available, but as you do not note your Country, I can’t answer that for your location.
However, as my power stations are primarily AC180 and smaller, and no expansion port, I use the Charger 1 from a 100Ah LFP deep cycle battery and any LFP will do the job.