Four Year Old Battery Died Suddenly - Load Test or Replace?

I performed this test tonight. I cranked for 15 seconds and the lowest voltage at the battery was 11.15. So if that means if the battery is OK and not weak, it went dead a few days ago from either a parasitic draw or driver error by not completely closing the door. If the battery was close to being weak, I would preemptively replace it to avoid stressing an alternator that is a challenge to replace because of its position under the engine.

Bing, how did you determine your battery is barely at its rated CCA? How do you measure CCA?

Also, thanks for the advice on best practices for maintaining a battery that is in storage. I will go back to pulling the battery and keeping it on a tender in the months the car is stored.

just out of curiosity, have you checked to make sure your brake lights are not stuck on intermittently? a faulty brake light switch would cause that.

also I have one of these that you might like to check out. SOLAR Digital 12V Battery and System Tester: Automotive

I have not checked the brake lights, and thanks for the info on the battery tester. That seems like a pretty comprehensive tool for a reasonable price.

I did not realize consumer-level testers were available. I always just went to the parts store for battery testing. I maintain multiple family vehicles and that would be a handy gadget to have.