At What Internal Resistance Should a Car Battery Be Replaced?

[Leonardo]

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.