This reply was originally posted by Bill on APC forums on 5/14/2015
Sorry for the inconvenience. The installation guide has diagrams on page 4 that show how to connect the battery. The guide does not state that the battery must be connected for the UPS to work however the unit is supposed to ship with a warning sticker attached that informs the users that the battery must be connected.
We apologize if the sticker was missing and again apologize for the inconvenience.