" they are tested to be drained down to nothing without risk of lowering the life of the battery." Did he say if they passed that test?
I think you will find a lot of disagreement with that statement.
The web site shows a life of 400 cycles when taken to 20% state of charge which is pretty typical. Life would almost certainly be much higher at lower discharges.
Sales folks throw out a lot things that are a bit of a stretch.
Don't take those very expensive batteries flat, or you will kill them early. The lower the discharge, the more cycles you will get. Most find 50% to be the best balance of life vs capacity.