2001 Dodge Intrepid brakes and brake assist failed

A national store/automotive shop recently installed a new/failed battery, the brake assist system failed leaving a hard pedal that would only stop with more than 200 pounds of pressure applied.
With no manager present and without a safe braking system, we were sent on our way and told to bring it (Intrepid) back when the manager was present. After 500 plus miles on the Interstate with no brakes the car was taken back to the Store where the manager advise us that changing the battery could not mess up the electronics involved in safe braking system and abs.
Two questions stand in my mind:
1) Can battery exchanges mess with the electronic braking and braking sensors on the Intrepid?
2) Was it improper or irresponsible for Wal-Mart to send an unsafe vehicle back to interstate traffic with no brakes?