Dell PowerVault NX3500 Getting Started With page 8

Reinserting the Battery
Align the battery with the power module and reinsert the battery. Ensure that
the battery is fully seated in the power module. If the battery is not fully
inserted into the power module, the battery front cover will not close properly.
NOTE:
Always connect the battery pack before connecting the power cable.
NOTE:
You will not observe the blind mate connectors as they plug into the
receptacle in the back of the power module, but a small amount of arcing may
occur when connecting the battery pack. This is normal and does not damage the
unit or present any safety concern.
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Getting Started With Your System