All of this sounds fine in theory as an explanation but was material fatigue actually why the technology was abandoned? Like you say, those complications are rare and the section that was quoted by the other commenter seems to imply that the opportunity to upgrade the patient's hardware was the real motivator (since obviously the opportunity to swap batteries wasn't a factor for the nuclear variant). It seems more like a question of if regular upgrades produce results significant enough to justify opening the patient up again after implanaing what's currently state of the art. Or is surgery obligatory in either case?