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 Contact Us Slendertone Optimum cannot be turned on? What happens if I connect the coloured leads incorrectly? What if my battery dies during a session? My controller will not charge Comments 0 comments Please sign in to leave a comment.