Having tackled the problem of independently powered and mobile artificial pacemakers, Medtronic raced against other companies to develop the next logical advance, an implantable device. The company partners with Wilson Greatbatch, an engineer, and William Chardack, a physician, to develop such a device. Although the first implantable pacemaker was created by Rune Elmqvist in Sweden in 1958, this device did not last more than a couple days. In 1960, Greatbatch greatly improved the battery life of such devices, first with a mercury battery, which could last up to two years, and later his co-development of a lithium-iodine source, which proved even more durable. The Medtronic Chardack-Greatbatch pacemaker becomes the first, long-lasting commercially produced implantable device.