What are the signs of a dead car battery?

[LeHayden]

The signs of a dead car battery include dimming vehicle lights, weak horn sound, and sluggish engine start. Methods to deal with a dead battery: 1. Jump-starting: Since the vehicle itself is a platform that uses and charges electricity simultaneously, jump-starting can be used to charge the battery after it dies. After jump-starting, driving for two to three hours under normal conditions can restore the battery's charge. 2. Using a battery charger: For vehicles that have been parked for a long time, using a battery charger to restore the battery's charge is a good method. However, it should be noted that operating a battery charger requires caution, as improper operation may damage the battery.

[VanAsher]

The symptoms of a dead battery are quite obvious. I experienced it just last week: when turning the key to start, the engine roared twice and then died, the dashboard flickered erratically like it was having a spasm, and the radio shut off and rebooted directly. After a few more attempts, even the clicking sound disappeared, and the headlights dimmed to candlelight levels. At this point, it’s basically a sign that the battery has completely given up. If you’re parked in a garage, you might still manage a jump-start, but if the car stalls on the road, the AC airflow will suddenly weaken, and the power windows will move as slow as a turtle. Later, a check revealed that the battery’s internal plates had aged, holding only a weak charge after just 30 minutes of charging, unable to deliver the 700A starting current. So, if you notice difficulty starting the engine, check the battery voltage immediately—don’t push it until you’re stranded on the road like I did.

[StThomas]

Here's a down-to-earth way to check if your battery is dead: Pop the hood and check if the electrode terminals appear whitish or greenish—that's a sign of sulfation. If the wipers jerk on their own when starting the car, or the hazard lights respond sluggishly, there's a 90% chance the battery voltage has dropped below 12V. A more obvious sign is when the remote key fob fails—pressing the unlock button gets no response from the doors, forcing you to use the mechanical key. Once, after leaving my car at the airport for five days, I returned to find the side mirrors stuck halfway folded and the onboard computer showing a voltage error code. Plugging in an OBD scanner revealed the voltage had plunged to 9.6V. This kind of static discharge can be revived with a charger, but if deep discharges happen more than three times, you'll likely need a new battery.

[VanDakota]

There are warning signs before the battery runs out of power. Last time when I started my car, the headlights suddenly dimmed for two seconds, the turn signal flashed faster, and the start-stop system stopped working prematurely. When I turned on the air conditioning, the airflow was noticeably weaker, and the electronic parking brake made a jerky sound when released—these are all signs of insufficient voltage. After testing, the battery life was only 23%, and the 12V voltage dropped to 10.8V under load. The scariest part was a voltage collapse while driving: the central control screen suddenly went black, the electronic power steering became heavy, and I almost rear-ended the car in front. A check at the repair shop revealed two short-circuited battery cells, and a full charge could only support 15 minutes of ignition operation. It's recommended that car owners always keep an emergency power source on hand, especially for older vehicles, which require extra vigilance.