Diagnosis time

My mother’s car battery has been dying. I borrow it from her so I can get to work on Sundays when the trains aren’t running yet. She likes to take it to a Shell station. They have done work on it, etc. They put a new battery in last June. After the car died a couple of times last weekend, we took it to her Shell place after it was jumped and running again. They said they could not diagnose the problem unless the battery was actually dead. They said they would have to keep it a few days to figure it out. The car kept starting for them. Is this totally bogus? We took the car back because we needed to run errands, etc. It was fine for a few days- started no problem up until Thanksgiving when the battery was dead. Got it jumped as in the other times when it died. Today had it towed the Shell station, but a neighbor suggested they were probably dishonest if they said before they needed to keep it a couple of days to see what was wrong. Could there be a reason why the diagnosis would take a long time? Or are they shysters?

There’s no way to tell whether they are “shysters” or not.

You need to have your alternator fully tested.

You need to have your main battery cables & their terminal checked for corrosion on both ends. Someone should also check for a key off parasitic battery drain.

Its no rocket science (though alternators can test good when they’re not), so maybe its time to try a new shop.

I’m not sure that a Shell gas station manned by pump jockeys would be the best place to track down an electrical problem no matter how much your mom likes the place.

Four things need to be done:

  1. Charge the battery fully. This may take 8 hours.
  2. Load test the battery.
  3. Check battery voltage with engine idling and accessories off. ~14-14.5V
  4. Test for parasitic load on the battery. < 100mA