Originally Posted by ceb
Why do you think the original battery was an AGM?
While registration is needed, what is more likely that something went wrong during the installation. These cars aren't like the old ones where you have two fat indestructible cables; our cars have very fragile electronics built into the cables that are frequently damaged if you just jank on the cables to remove them from the posts.
It doesn't matter if the car is or was using an AGM or not. i doub't the cables are an issue since it was able to start when charged. Maybe this will show some insight to Battery Registration.