Slendertone Optimum switches off during a toning session? Recharge the batteries for 3 hours, once charged start your toning session again. If the problem persists please contact us. Related articles The controller does not switch on when the Power button is pressed What happens if I connect the coloured leads incorrectly? How long does the battery take to charge? Optimum Instruction Manual Comments 0 comments Please sign in to leave a comment.