How to Test Whether a Battery is Good or Bad?
4 Answers
Methods to test whether a battery is good or bad: 1. Visual inspection: When a battery has problems, there are visible changes, such as leakage, swelling, bulging, or severe damage. If these signs are present, it can be determined that the battery is faulty. 2. Connect a load: For example, for a 12V battery, you can connect a 12V light bulb or motor and check if it operates. If it doesn't, the battery may have issues. 3. Connect a battery charger: Observe the charger's response. If the battery is good, the charger will show a red light and start charging. If the battery is faulty, the charger will only show a green light, and the battery may heat up. 4. Use a multimeter to measure voltage: Connect the red probe of the multimeter to the positive terminal of the battery and the black probe to the negative terminal. Set the multimeter to DC voltage mode and measure the voltage to see if it matches the rated voltage.
A couple of days ago, my neighbor's car wouldn't start, so I helped them check it out and took the opportunity to teach them how to diagnose battery issues. Using a multimeter to measure the static voltage is the most straightforward method—after turning off the engine, connect the probes to the battery's positive and negative terminals. A normal reading should be 12.6 volts or higher; anything below 12.2 volts is a warning sign. If the voltage drops below 10 volts during startup or even rebounds to 9 volts, the battery likely won't last through winter. Repair shops have a more accurate tool called a battery tester, which simulates the load current during startup and provides a health report in five minutes. Regular observation is also important: white powder on the battery terminals indicates leakage and corrosion, while bulging on the sides is a clear sign it's time to replace it. Lead-acid batteries typically last three to five years, so replacing them when the time comes is the most hassle-free approach.
I used to always have dead battery issues when modifying cars, but now I've developed a habit: pop the hood and check the battery inspection window first. A green glow in the little transparent circle means it's healthy, but if it turns black, it's time for replacement. Cars with auto start-stop systems are particularly picky about batteries—I learned this the hard way when a regular battery died in just three months. Switching to an AGM battery specifically designed for start-stop systems solved the problem. I use a battery tester to check the CCA (Cold Cranking Amps) value—if it drops below 70% of the rated value, it's risky. Once before a long trip, I measured the CCA at only 200A and rushed to replace it, avoiding a potential breakdown on the road. The old battery could still be traded in for a 50-yuan discount on a new one.
Last month, my car battery suddenly died, making me late. I learned a few emergency diagnostic tricks: if the headlights dim noticeably when starting the engine at night, it indicates insufficient power. A sluggish response from the remote key is also a warning sign. Using the simplest voltmeter, attach the red clip to the positive terminal and the black clip to the negative terminal. A reading below 12.4 volts before starting or below 13.7 volts after starting is abnormal. I now keep an emergency jump starter in the glove box—about the size of a cigarette pack, it can be a lifesaver in critical moments. When replacing the battery, remember to disconnect the negative terminal first, then the positive, and reverse the order when reconnecting.
