2014 Corolla - Bad Alternator or Bad Battery?

[Corollatronic]

@NYBo

The Toyota tech was mistaken. There could be a bad diode in the alternator. That could drain the battery and not illuminate the battery light. This fits your symptoms.

@Mustangman

Oh, and stop letting the dimwits at Autozone test your 2 year old car. Its cost you a battery that probably didn’t need replacing only recharging. Let real technicians diagnose the actual issue rather than throwing parts at it.

Actually, the “dimwits” didn’t cost the OP a battery that probably didn’t need to be replaced. It was apparently the OP who decided to buy the battery (at a competitor, no less). The equipment we use is probably as sophisticated as what the dealership would use, and it walks the person using it through the proper steps. If the battery is too discharged to test, the meter will state that on the display.

I had no problem buying the battery from Walmart because their 90 return policy covers batteries, so if my old battery was still good then I could just have returned it.

I got off the phone with Autozone and they tested the battery, and it is bad. Getting a new one wasn’t a waste of money. I have a friend with a voltmeter who will bring it to work tomorrow and we will run our own diagnostic to see what the voltage readings are. I’ll update tomorrow with the results.