Tinkerer, we don't know..... The only way to be as close to absolutely sure as possible is to buy from the main dealer.
Carparts4less's prices, once the mbclub25 discount is applied, are only slightly less than ECP's (for batteries, anyway). The difference for me is that there is an ECP store about a mile away, so I go there if I'm in a hurry. At the moment I am; the battery in the dragon's car has just died.
E55BOF