New battery and alternator Volt meter measures zero

Recently replaced the alternator and battery at the dealrship. Volt meter now registers zero where prior to and during failure it hovered around 13 (best guess). Simultaneous use of A/C, heated seats, radio, wipers, etc. Don't seem to affect power delivery as they did during failure. The mechnic is telling me the zero reading is perfectly normal but I think he's giving me a line.

Could it be the battery and alternator are not communicating they way they should? What questions should I ask of my mechanic?

BTW, you solved a fuel-pump dilemma on my 1985 VW Cabriolet a long time ago. I asked every neighborhood mechanic to replace the pre pump and they pretty much shook their heads and said (effectively), "Cars don't have two fuel pumps. You don't know what you're talking about." I nursed it to a VW mechanic and asked, "Will you change my other fuel pump?" And he said, "No problem." That's the power of knowledge.