I have a 2004 Mazda 3. It got a new battery just over 2 years ago. About 8 months ago, the alternator died and I had that replaced and everything seemed fine in the months since then, including as recently as last weekend.
A few days ago, the car wouldn't start. When turning the key, absolutely nothing happened. Battery didn't even have enough energy to unlock the doors via key fob. Called AAA to take a look. Technician gave the car a jumpstart, but lights were flickering and the car died again shortly after jump kit was disconnected from battery. He thought the alternator was to blame.
This morning, we had the car towed to a repair shop. To get the car out of my garage and onto the truck, tow driver had to jump the car and leave the kit connected while driving the car. Even doing this, the car would die within seconds of ignition each time he started it, so it took a few attempts.
Repair shop ran a battery diagnostic and discovered that one of the battery cells was totally dead, and the cause was likely the added strain from last year when my alternator failed. They replaced the battery and reported that the alternator voltage was fine. The car drove fine all the way home (~30 minutes in slow Chicago traffic).
However, I am suspicious that my problem has only been fixed in the short term, and the car will start dying again soon. I thought that, after jumpstarting a car, it would run with a totally dead (or even disconnected) battery because everything would be powered by the alternator. That did not seem to be the case when the tow driver was getting the car out of my garage, or when the AAA guy was trying to diagnose the issue.
Am I paranoid or ignorant? Could a battery with a dead cell really have made the car die even after a successful jumpstart? Or should I be expecting more issues to crop up in the near future?