Ran out of replies on the ol’ corpo’ account. On the plus side, on this account I’m allowed to say “fuck” 
PO Box addresses are pretty much always formatted:
PO BOX #XXXX
CITY NAME
STATE NAME, ZIP CODE
So it’s self evident that it’s a post office.
You probably meant “freight forwarder” then, and I have no idea how your frieght forwarder would feel about shipping a large lithium battery across the border 