In my mind (and I'm assuming in his mind too) the idea could have been to use the battery as an extension of the finger? not really taking into account that it could get stuck.
BUT: I may not really know much about batteries and its properties. But after hearing how a single battery into the water or under some earth can cause a huge disaster pollution-wise, I wouldn't consider having that inside my own body.

Guys shoving up shits other than literal shit up their asses is hardly a new phenomena. But damn girl, from all the tubular/cylindrical things u couldve chose from, u chose AA fucking battery??? I understand wanting to create medical emergency as part of the plot, but wouldnt other things with no flared base be enough??? Battery is, on top of that, corrosive and small as heck??? You're not gonna feel jackshit girl wtf. But eh, I guess it makes the trip to the ER actually, very justifiably necessary tho, so... all's well that ends well???
Anyway, what a great start. Cant wait for the rest lol