Back in the '90s, there was a KLM (Martinair?) 767 enroute from AMS to JFK in which the electrical systems shut down one by one. They landed in KBOS with no flaps, etc. A battery may have been intermittent or disconnected.
The plane was then ferried to Boeing, where they could find nothing, IIRC. I never did see a full report on it. Does anybody have a ref?