I wouldn’t repair a car that killed itself over a 12 V battery dying. Sadly I missed this thread. My immediate response would be to buy a replacement 12 V battery as first recourse. Just because you were able to get a trickle charger to raise the voltage up to where it says it’s full doesn’t necessarily mean the 12 V is now healthy. Might be worth investigating first whether the 12 V is truly in good shape and go from there.