1. Measure the open circuit voltage of the battery.
2. Add a load and measure the battery charging voltage. and the battery charging current.
3. Internal resistance = (battery open circuit voltage - battery charging voltage) / battery charging current
I have been in this industry for many years! Haha~~
There is no way to test it with a multimeter. There is a simple method. According to q=i square*r, heat is equal to the square of current × resistance. can use a few batteries in parallel to see the heat and deduce it. I always use an internal resistance tester in my shop. As long as it is above 30 milliohms, we will eliminate it directly. Most of those purchased from a certain treasure store are above 35 milliohms. Automotive grade batteries are usually around 25. The larger the capacity, the greater the internal resistance.e 18650 is much larger than big cells due to its small capacity. Let me tell you about the internal resistance of the lithium battery I produced: it used to have an internal resistance of 19 milliohms for 2200mah, but now it uses 2500mah and the internal resistance is 25 milliohms. These are grade A batteries for electric vehicles, and grade B batteries are generally above 30 milliohms. I typed it word for word, please accept it. Without an internal resistance tester, it cannot be measured