I’m leary of a mechanic who says, “Alternators, batteries and starters can’t be accurately tested out of the car on a bench!”
Is that or any part of it true?
No.
Tester
Sure they can be tested but what he was most likely trying to say is there are other things associated with the devices in the vehicle that can effect their proper operation. Particularly with the wiring between them. For instance, an alternator may work fine on the bench but have no output in the vehicle.
Yes, but if the alternator tests good on the bench and doesn’t work in the car, then it’s not the alternator. Bench testing can eliminate possible causes. I’m think some mechanics pooh-pooh bench testing because they aren’t set up to do it themselves.