“A small device can modify pacemakers so that they use kinetic energy from the heart’s beating, converting it into electricity to keep the batteries charged. The researchers added a thin piece of polymer to existing pacemakers, which converts motion into electricity, they explain in Advanced Materials Technologies…”

Source: https://www.technologyreview.com/the-download/612893/future-pacemakers-could-be-charged-by-our-heartbeats-rather-than-batteries/