How to Determine if a Battery is Good or Bad?
3 Answers
To determine if a battery is good or bad, you can use the following methods: 1. Check the battery status through the observation hole. If you see green, yellow, or black, it indicates the battery is in good condition. Yellow means the battery capacity is insufficient, and black means the battery is damaged. 2. Assess the battery's usage state. If the battery does not hold a charge, frequently runs out of power, or cannot be recharged, it indicates the battery is damaged. The functions of a battery are: 1. To power the engine starting system, ignition system, and the vehicle. 2. To supply power to the vehicle's electrical equipment when the engine is off or at low idle. 3. To mitigate impact voltage in the system and protect the vehicle's electronic devices.
As a novice who often takes care of my car myself, judging the condition of the battery is quite simple. Start by checking the exterior: Open the hood and inspect the battery terminals for white powdery corrosion or signs of leakage. A bulging case also indicates internal issues. When starting the car, listen to the sound—if the engine cranks very slowly or makes a clicking noise but won’t start, it’s likely the battery is dead. A household multimeter can measure voltage: Connect the red and black probes to the positive and negative terminals, respectively. A resting voltage of 12.6V or higher is normal, while anything below 12V means it’s time for a replacement. Even without tools, you can test with headlights: Turn on the high beams and start the engine—if the lights dim significantly, the battery is weak. I also recommend checking like this every six months, especially in cold weather when batteries are prone to failure. Early detection can prevent being stranded on the road.
Over the years of working in auto repair shops, I've learned more professional methods to check battery health. The most reliable way is to conduct a load test with a battery tester: simulate the high-current discharge during engine cranking, and if the voltage drops below 9V, the battery is confirmed dead. When measuring static voltage with a multimeter, anything above 12.6V indicates good health, while below 12V means immediate replacement is needed. However, after charging, you should test the voltage recovery speed - if it drops quickly, it indicates high internal resistance and poor condition. Also, check for loose or corroded battery terminals, as corrosion can obstruct current flow. From experience, conventional lead-acid batteries last three to five years - remembering to replace them periodically saves trouble. Don't overlook details like electrolyte levels for wet batteries, and even maintenance-free batteries should be inspected for any external abnormalities.
