At What Internal Resistance Should a Car Battery Be Replaced?
4 Answers
Car batteries should be replaced when their internal resistance exceeds 10 milliohms. Here are the relevant reasons: 1. Normal internal resistance range for car batteries: Most cars use 12V60Ah or 12V65Ah batteries, with internal resistance typically between 4 to 6 milliohms. 2. Effects of increased internal resistance: The greater the battery's internal resistance, the smaller the current, which can affect the normal operation of the vehicle. 3. Methods to determine battery aging: Voltage level, as voltage is what drives charge to produce current. Voltage is further divided into open-circuit voltage, charging voltage, and discharge voltage. For a 12V battery, the open-circuit voltage is generally above 13V.
I once had battery issues while driving, and when the internal resistance increases, it's time for a replacement. Internal resistance is usually measured in milliohms. For a new car, it ranges from 3 to 5 milliohms. If it exceeds 8 to 10 milliohms, it should be replaced; otherwise, starting the car will be very difficult, especially during cold winter starts when it cranks for a long time. I've used a simple tester myself, and when the value is high, the car starts slowly or even fails to start, and it can also affect the brightness of the lights. Regular maintenance should include periodic checks to avoid waiting until the battery is completely dead before replacing it, preventing breakdowns on the road. Battery life is typically around three years, and replacing it early when internal resistance is high saves both hassle and money. Remember to match the new battery model to avoid issues caused by non-compliance. You can also check the voltage drop in the car; if the voltage drops below 9 volts during startup, it's another sign of aging. It's best to have a professional shop confirm before replacing.
As someone who enjoys DIY car repairs, I often measure battery internal resistance to determine if a replacement is needed. A high internal resistance value indicates battery aging. Generally, if a testing tool like a multimeter shows over 7 milliohms, it's time to prepare for a replacement. The benchmark for new cars is 3-5 milliohms. The exact value depends on the vehicle model, but if it exceeds twice the initial value, action should be taken to avoid affecting power supply stability. Ensure the battery is fully charged when measuring for more accurate results. High internal resistance can easily lead to insufficient discharge current, causing starting difficulties, and may even damage other circuit components. Make it a habit to test every six months, combined with voltage checks: a resting voltage below 12.4 volts also signals replacement time. Timely replacement can prevent roadside failures, and choosing a high-quality brand can extend usage cycles and reduce frequent replacements.
Years of driving experience have taught me that when the battery's internal resistance gets high, it's time to replace it—no need to obsess over exact numbers. For instance, an internal resistance value around 10 milliohms is acceptable, but if it's doubled compared to when the car was new, problems arise. If the engine struggles to start and the lights flicker, replace it immediately to avoid trouble. I remember one time when high internal resistance left me stranded on the road—I regretted not replacing it sooner. Considering the battery's lifespan, don't wait if it's over three years old. Regular maintenance, keeping it clean, and topping up the electrolyte can buy some time, but eventually, it must be replaced for safe driving in advance.
