At What Internal Resistance Should a Car Battery Be Replaced?

[Corinne]

Car batteries need replacement when the voltage after charging is less than 13 volts or the voltage after discharging is below 10 volts. Car batteries are categorized into conventional lead-acid batteries, dry-charged batteries, and maintenance-free batteries. The commonly referred to 'car battery' typically denotes a lead-acid battery, with a normal service life ranging from 1 to 8 years, heavily dependent on vehicle conditions. Conventional batteries have plates composed of lead and lead oxide, with an electrolyte of sulfuric acid solution. Dry-charged batteries, fully termed as dry-charged lead-acid batteries, feature negative plates with high energy storage capacity, capable of retaining charge for up to two years in a completely dry state. Maintenance-free batteries, due to their structural advantages, exhibit minimal electrolyte consumption and generally require no distilled water replenishment throughout their service life.

[ChloeAnn]

Regarding when to replace a car battery based on internal resistance, I often encounter this issue during repairs and believe the key points are the numerical values and daily performance. A new battery typically has an internal resistance between 5 to 10 milliohms, performing well. When the resistance rises above 15 milliohms, you may experience hesitation or delays during startup, which is a sign to seriously consider replacement. If it exceeds 20 milliohms, replacement is absolutely necessary—otherwise, the car may struggle to start in cold weather. I also recommend combining this with a cold cranking amps (CCA) test; for example, if the CCA drops below 70% of the original factory rating, it’s another warning sign. Keeping the battery terminals clean to avoid corrosion can help slow the increase in internal resistance. Regularly checking with an internal resistance tester is convenient, inexpensive, and helps prevent issues. Remember, the average battery lifespan is three to five years—addressing problems early avoids roadside breakdowns and ensures safer driving. This is based on my practical experience, and I hope it helps you.

[WalkerLynn]

As a car owner with years of driving experience, I've personally experienced the troubles caused by high battery internal resistance. When the resistance rises to around 15 milliohms, the car starts slower or occasionally fails to start, just like last week when my car got stuck in the supermarket parking lot for quite a while before starting. I recommend replacing the battery as soon as the internal resistance exceeds 15 milliohms, as waiting until it reaches higher levels like 20 milliohms poses greater risks. You can easily test it at home with a battery tester, or get it checked for free at a repair shop. My habit is to check it every autumn, as winter poses the greatest challenge to car batteries. Car batteries typically last four to five years, and rising internal resistance is a sign of aging. Don't wait until it completely fails; acting early can save you towing fees and ensure safety. Sharing this little tip to make driving smoother.

[DiCassidy]

I think a car battery should be replaced if its internal resistance exceeds 15 milliohms. My experience tells me this, because high internal resistance can cause delayed or failed starts, especially noticeable during morning cold starts. Simple testing tools are sufficient for measurement - if the reading rises significantly, make the replacement decision. Car batteries typically last about four years, so don't delay replacement to avoid breakdowns affecting your daily commute.