"My local post office demands that you tell them what is inside any parcel you attempt to send."
I recently received some 300mah Ni-Mh batteries from Farnell that I wanted to return as they were not the desired form factor (my mistake). I then realised that I was almost certainly going to have a
argument discussion with the Post Office counter assistant when they asked "any batteries?". I was in no mood to be a barrack room lawyer*** - so they went in the "useful bits" box.
*** The Royal Mail regulations permit batteries of that capacity as long as they are in unopened manufacturer's packaging.