I know about 6 people who have had the Nevro HF10 implanted. For half of them the "permanent" one did not perform like the trial one did. Why? I can only guess that the leads were situated differently than the trial ones. Mine works so well that I forget to charge it...until my back starts to hurt. Then I have that "duh!" moment as I smack myself in the forehead with the heal of my hand.