While driving the car lost power and came to a dead stop. Won't start

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Last week engine turned over but would not start, but then did. Happened again this week and Autoelectrician not MB expert but tested sparking. OK. All lights working, not battery. I read it could be remote batteries getting old and not reading code so followed advice and car started. (Happy!) Then today car just died and came to a halt while driving. Had to tow home. What could this be?