They might have been checked at some stage, but if you have enough intel, you can figure out at which stage to insert the vulnerability. But i have seen lots of fun ideas on how this could be done. The fact that its apparently alkaline batteries, makes it interesting tho. Unless it was fake batteries with something inside them.
You could also try to make it so that the people who check the devices, only get to see good ones.
If the world were black and white then he would be a democrat. In actuality tho the new guy is a deranged and delluded self glorifying wreck of a weirdo. Read his/the incidendts wikipedia article.