What is the Standard Battery Sorting Accuracy for 18650 and 21700 Cells?

In the realm of battery manufacture and recycling, being able to accurately sort lithium-ion cells is crucial for quality as well as safety and performance of the final product, and it’s important for cells such as the 18650 and 21700 which are the workhorses for consumer electronics, EVs, and large storge batteries.
Battery sorting machines need to ensure that end cells in a pack end up with similar voltage, capacity, internal resistance characteristics, and overall efficiency comes from good sorting accuracy. But what does standard even mean in this context? To start with, battery sorting accuracy is dependent on:
Cell Type/Size: 18650/21700, although both are lithium-ion, are notably different in size and energy potential;.
Internal Resistance and Voltage Consistency: A common characteristic on the cell to base the sort is voltage, and a big difference in internal resistance or voltage effectively leads to poor sorting.
Sorting Technology: Machine/technologies differ from IR absorbance sorters to pogo pin testers on a powered conveyor for example, and sorting approach.Accuracy: Some methods are more no precise than others and some machines are better suited to be fairly precise with what they measure.
Sorting tolerance: In general battery sorting machines have a tolerance that they are going to sort based on, typically a range of 1% to 5% internal resistance and voltage/voltage drop based upon the type of sorting machine, and the application they suit. More expensive machine tend to have stricter sorting tolerance and often sort in 0.5% steps for more important applications.
Standard Sorting Accuracy for 18650 and 21700 Cells
For 18650 and 21700 cells, the sorting accuracy typically falls in the following ranges:
Voltage – within 0.05V to 0.1V.
Capacity – the capacity of lithium-ion cells in another important parameter impacting sorting accuracy measured in ±2% to ±5% of the rated capacity. High-end sorting systems approach ±1% for cell applications like electric vehicles and energy storage systems.
Internal Resistance – the degree to which a cell’s internal resistance impacts its performance is critical. Sorting machines for 18650 and 21700 cells typically have an accuracy range of about 1% to 3% for sorting internal resistance. Cells with a significantly different internal resistance will not work well if placed together, for example, in a battery pack of a mobile device, which will shorten the lifespan of the battery very much and it will die much sooner than expected.
Why Accurate sorting
Battery Performance – by sorting cells that perform similarly, the overall performance of the completed battery pack is improved with good energy efficiencies and longer life cycles.
Safety – sorting incorrectly can lead to a number of hazards including but not limited to leaks, over heating and in certain dangerous cases Chemical Heat runaway. By maintaining sorting at certain levels, the chance of a battery pack exploding goes down immeasurably.
Cost Efficiency – better sorting equals less waste cos by properly filtering and grouping cells with cells of similar resistance/capacity, the chances of short life cycles are lesser, and the margins open for pairing a not as great cell is avoided, by not selling “overcharge allowance battery cells”. By pairing them with underperforming cells they cost batteries and can be terribly expensive if not correctly scrutinized.
Conclusion
In summary, the accuracy of 18650 and 21700 cells is generally around 0.05V to 0.1V and typically within 2% to 5% for capacity and 1% to 3% for internal resistance, with some high-end systems offering better accuracy depending on the application. Cells with a varied internal resistance typically make terrible batteries, and there will be an unexplained lack of cycles at the most. Basically those cells are not cells at all; just mini burglar alarms waiting to go off and spoil your dream. Invest in a decent accurate machine with tight accuracies and you are invested in producing good bats.