Mustek PowerMust 1000 On Line(1K) User Manual page 10

(1) Use the battery pack with voltage: 36VDC for PowerMust 1KS On Line(3 pcs of 12V
batteries). Connection of batteries more than or less than required will cause
abnormality
⑵ One end of the external battery cord is a plug for connecting the UPS and the other
end is a plug for connecting the user battery pack
⑶ Do not connect the UPS to any load yet. Then, connect the power cord of the UPS to
supply utility power to the UPS to make the UPS operation in utility power mode.
⑷ connect one plug of the external battery cord to the user battery pack, then connect
other plug to the external battery socket on the rear panel of the UPS to complete the
connection procedure and the UPS will start to charge the battery pack
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