[Tannaton]

I would disconnect the battery negative lead and then try again, connecting the battery charger directly to both battery terminals.

Your 4 amp charger is at the low end of charger ratings and I suspect that the systems in the car that power up for a few seconds and then go to sleep when the battery is connected or doors opened etc. are consuming all of the charge and none going to the battery. So if you connect the charger only to the battery, it will get the full dose. You won't affect the BMS system as this should reset itself when the battery is disconnected for more than a few mins anyway.

If you can, as said above, I'd leave it like that circa 48 hours and try again. You could temporarily reconnect the negative lead after say 4 hours just to see if the battery is taking a charge and it will sustain the basic systems, if it won't after 4 hours then you should inform the battery's next of kin.........

On a 2012 car it's not inconceivable you are still running on the original factory battery in which case you've had your monies worth.