What are battery cell grades? How do manufacturers use cell grades in the manufacturing of batteries? How do the different grades affect the quality of a battery? In part 2 of this article series we will continue where we left off and look at the battery cell grade classification system that battery manufacturers use during the process of collecting raw battery material, developing design specifications, and assembling packs for various consumer and industrial applications.
Battery cell grades are a classification system that manufacturers use to distinguish the benefits of capacity and runtime. Before I unpack that answer we need to understand that battery grades are not a measure of quality! Battery grades do not imply that one grade is “better” than another but a reflection of capacity and internal resistance at different price points. Before I continue with cell grades it is important to understand capacity and internal resistance.
Battery capacity quantifies the total amount of energy stored within a battery. Battery capacity is rated in Ampere-hours (AH), which is the product of: AH= Current X Hours to Total Discharge. Battery capacity is measured in amperes, which is the volume of electrons passing through the batteries electrolyte per second. A milliAmp hour (mAh) is the most commonly used notation system for consumer electronic batteries. Note that 1000 mAh is the same as 1 Ah. (Just as 1000mm equals 1 meter). In essence more capacity equals longer runtime between battery charges.
Internal resistance, known as impedance, determines the performance and runtime of a battery. It is a measure of opposition to a sinusoidal electric current. A high internal resistance curtails the flow of energy from the battery to a device. Internal resistance is caused primarily from the opposition of current by the electrolyte that resides between a battery’s two electrodes.
Now battery cell grading is a process of categorizing cells into grades (Grade A, Grade B, and Grade C). Every grade is important to the manufacturer, meaning there is not one grade that is better than another. In fact every manufacturer wants to make and sell each cell grade because of the unique differences of each grade and because each cell grade has a specific market and device segment.
As mentioned above cells are always categorized to be graded A, B and C but there is not a single manufacturing standard for categorizing cells; each manufacturing factory may have their own standard so thus cell grade categorization is not necessarily scientific.
For example, Li-ion cell 053450, some companies may categorize the cell as follows
Grade A--- capacity above 1000mAh, internal resistance below 60mΩ
Grade B---capacity 900 to 1000mAh, internal resistance 60mΩ to 80mΩ
Grade C---capacity below 900mAh, internal resistance above 80mΩ
But for some companies with better production lines and capability, they may have higher capacity cells so they may categorize cell 053450 as follows:
Grade A--- capacity above 1100mAh, internal resistance below 60mΩ
Grade B---capacity 1000 to 1100mAh, internal resistance 60mΩ to 80mΩ
Grade C---capacity below 1000mAh, internal resistance above 80mΩ
One generally accepted conclusion can be drawn from these two examples and that is grade A cells have the longest runtime and cycle life, grade B has the second longest runtime and cycle life and grade C has the third longest runtime and cycle life.
Until next time Dan Hagopian www.batteryship.com
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