In my opinion, they are meaning the Battery Connection, as in for safety, in case the inverter section is turned on you won't get zapped when connecting your AC output. See on Page 5 of the manual, they refer to a DC protector:
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Battery Connection
CAUTION: For safety operation and regulation compliance, it’s requested to install a separate DC over-current protector or disconnect the device between battery and inverter. It may not be necessary to disconnect the device for some applications, however, it’s requested to have over-current protection installed. Please refer to the typical amperage in the table below as required fuse or size of the breaker.
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I would also disconnect PV solar input (at the combiner box disconnect, or wherever), as a safety precaution for while you're making the AC connections, since PV input could power the inverter (if the inverter supports batteryless operation).
Of course it goes without saying, to also make sure the grid power incoming circuit is not live when making the AC input connection. Just a little common sense (and a voltmeter to check) and make sure there is no surprise power anywhere while you're fastening the connections.
