I have a set of Z-Lynk headphones that will not charge. The charge light is on, but as soon as you disconnect the power and try to turn them on nothing. If I leave the power cord connected, and turn them on, they turn on but shut off as soon as the power cable is removed. Has anyone ever replaced the battery. They are out of warranty and will cost at least 21.00 plus shipping and parts if repairable to send them back for repair.