I just purchased this vehicle and was checking the battery voltage at the terminals in the trunk and found this unplugged connector next to the battery’s positive terminal. Anyone have any ideas what this is for and where it’s supposed to be connected.

I also found out that the previous owner replaced the oem battery with a lead acid battery instead of AGM. How bad is that? Not sure when it was replaced. Should I replace it with the proper specification AGM battery immediately?

Click image to enlarge

Click image to enlarge

I have the same plug which is in the same place and not bothered to even look further.
Regarding battery, if you're using start stop function acid batteries will give up earlier as they need longer time inbetween starts of engine. But IMHO keep it until it runs you can feel the point when it starts to fail.

Its to do when the car is delivered to the dealership. They disconnect it at PDI, does not serve any function. I asked this question years ago regarding my Sport

From the WM above:

“ When the vehicle leaves the factory, a transit relay is fitted to the primary battery positive terminal. The transit relay is connected to the CJB (central junction box) which limits the electrical functions to essential items only, to reduce loads on the battery. The transit relay provides battery power to the BJB2 (battery junction box 2) which supplies the starter motor, generator and the positive jump start terminal. The transit relay must be removed from the vehicle during the PDI. For additional information, refer to the PDI Manual.” “If it ain’t broke, don’t fix it” -where’s the fun in that?