I watched a video from weber university and noticed that the fast dc charging ports seems to be directly connected to the battery (with a contactor between). This got me thinking that maybe it could be used as a backup battery for a hybrid inverter.

Don't have enough information, but seems that the voltage is compatible with inverters using a high voltage LG rheus battery (300–400 V). Was thinking it would only need blocking diodes to prevent the battery from charging, since a charge controller would be a more involved project. Not only providing the correct charging profile, but maybe also needing to emulate the bms of the battery.  A 25A 600V diode shouldn't be hard to get.

Not sure if the inverter expects the bms to be active to use the battery? On mine the battery seems to be in parallel with the output from the pv panels.