So I noticed this issue a few weeks ago... Battery holds charge at 13.5 with the car on, when coming to a stop... the voltage drops into the 12's. I popped open the backseat to notice the old battery was leaking acid all over the place. Bought a new AGM battery today, popped it in... behold the same issue. Except this time, it reads 13.6 with the car on... 11.8 off. Checked the alternator, reading 14.1... I can't think of anything besides the fuses, relays... anyone have any suggestions? Perhaps someone who's had the same issue?