The battery would be SLA (sealed lead acid), and not a Lithium flammable type. For cargo planes, there can be rules about Lithium. For a Post Office, their main concern other than that, is with dimensions or weight of the item. A big UPS would likely exceed any of their available options. Even some couriers can object to carriage of a UPS, just from the weight of the thing.
For the fossil record, you should include the model number of this product in a post, in order that future generations can benefit from the discussion thread. We don't even know what SKU bracket this thing is from, cheapest (10% failure rate) level, mid-range level, or "business class extra expense" ones. A double-conversion unit with a fan that runs all the time, is the type popular in Server rooms (the switchover time on those is 0 milliseconds, versus the typical 2 cycle switching time of the SPS Standby Power Supply type popular for cheap ones). My last employer had one like that (double conversion) for our little server and the tape autoloader (that was so our single IT guy could go home at night to his wife and four kids).
If you don't want to include the model number (written on the bill), then just tell us the price before tax. That will establish its credentials as a piece of crap.
Paul