Sentra Weak Battery Flickering Lights

That sounds familiar! I had similar symptoms on my old BMW 3 series, although it was a diesel. Weak starts and flickering lights drove me crazy. Have you checked the battery terminals for corrosion? Sometimes a poor connection can mimic a bad sensor. But if you already checked the voltage, it's likely a defective battery sensor.

I checked the terminals, and they seem clean. I am not an expert on car electrics. Can a defective sensor really cause the battery to perform so poorly? What kind of impact does that sensor have on the battery's charge?

Yes, absolutely. The sensor provides crucial feedback to the car's charging system. If it's sending incorrect data, the alternator might not be charging the battery correctly, leading to the issues you're seeing. It's best to have it properly diagnosed with the right tools; my mechanic immediately knew what to do. I would recommend you go to a workshop for proper battery testing.

Based on your recommendation, I took the car to my local mechanic. The diagnostic confirmed a faulty battery sensor, as suspected. The repair, including the sensor replacement and labor, cost 315€. I am grateful for your help in pointing me in the right direction.