I too have a partally ruptured disc in my neck and middle of my back that I sustained through a very hard slip-fall, on the back stairs many years ago.
I bought mine at a different site but it was more expensive with the AC adapter. It didn't require a doctor's prescription either.
Please search other sites for the best price, but this one, is one of the best that I've seen. (get a bottle of GEL) as it will extend the pads for many more weeks.