2-5A is enough if all the accessories are off.
I'm currently using a cheap manual (thankfully) 2700mA charger, but I plan to flash some newer cars (EDC17, MED17, SIMOS 10/12/18), and don't want to take any chances. Also, my flash tool doesn't show voltage while flashing, which is bloody annoying.
But I agree, for ME7, MED9, etc.., I expect 5A to be plenty.