Drained battery

I replaced my alternator. A few weeks after, my battery stopped staying charged while driving. An error code will come on "ABS" "check brake system" then all lights on dash will go out and eventually the car will turn completely off. Since this has started I have taken the alternator off the car twice, taken it back to where I purchased, and had it tested on a machine. It passed as a good alternator both times. Replaced fuses, wires from alternator to battery, battery terminals, and the main belt for the car. I have gone through 5 batteries in roughly 6 months, and something is killing these batteries. Before replacing the battery we have them tested and they have all had bad cells. I'm needing guidance on what to do next. Please help!