My 2001 Saab 9-5 automatic transmission wouldn't start at least once a

week. What is wrong with it? It would not start at least once a week.
I'd bang the battery and then try again and it would start.
The battery is new, I got it switched with another new battery because I thought the first one was defective.

I took it to a shop.
They said there was nothing wrong with the starter, battery terminal, battery relay, and alternator.

What can be wrong with it?

When it fails to start, there is no noise at all.

If u checked voltage then might be starter.