Battery voltage drops to 0 when high load and then recovers

Morning.
I took the car to the mechanic for a bearing change and to change the airbag clockspring.
The mechanic told me he would see if the car has any electrical problems before changing the clockspring, so it won’t break down again. Just yesterday he told me that he had a new fault: when he uses the power windows or the AC, the voltage goes down to 0, and after 5 seconds of not using them it recovers completely, all this with the car started.
I had noticed that, logically, when I use these things, the voltage drops from 14.5 to 14.3 or similar, but not to 0.

I don’t know if he’s exaggerating, or if he’s just not looking right, because it’s never happened to me before, and it’s just happened with the car in the mechanic’s shop. I don’t think it was the bearings being changed because nothing electrical is touched.

He told me that he had checked the fuses, and that there was nothing wrong, so I don’t know if he is exaggerating or if there is really a new problem (which is very strange and doesn’t fit with any information I looked up on the internet and that the mechanic has been trying to fix for 2 days)

P.D.: the battery is only a month and a half old.

What is happening there? Can it be a bad alternator? A bad battery (again)? A short?

The car is a chevy aveo from 2012