What is C-Rate?
C rate is defined as the measurement of the rate at which the battery cell can be charged or discharged in relation to the cell capacity.
The C rate does not change based on the capacity of the battery cell, instead it is an intrinsic property of the battery cell itself.
C rate is calculated as a multiple of the Capacity rating of the battery.
Let me make it easier to understand with examples :
A battery cell with a rated capacity of 2 AH and a maximum continuous discharge current of 4 A has a C rate of 2 .
This battery would be known as 2 C battery.
We get C rate by dividing the maximum discharge current rating by the capacity, which is calculated as :
C rate = 4A divided by 2Ah = 2
If the same cell has a maximum discharge rating of 6 A instead of 4 A, it would give us 3 C battery.
If maximum discharge rating is of 10 A, it would give us 5 C battery.
But if it had a capacity of 5 AH instead of 2 AH, then it would be back to a 2 C battery.
Got it? If not, try working those examples out on paper using the same equation as above.
The C rate is important because it is used to compare the relative power of cells, even when cells have different readings.
A big 10 AH cell might be rated for 10 A maximum discharge while a smaller 2.5 AH cell is only rated for 5 A discharge. At first it might seem like the big cell is more powerful, as it can provide twice the current that the small cell can provide right? However it is the smaller cell that is more powerful relatively, as it has a higher C rating.
The smaller cell has a C rating of 2 while the larger cell has a C rating of 1.
If we combined four of the smaller cells together in parallel, we would make a 10 AH battery that will have its rate at 20 A maximum discharge.
Now lets compare that to the original bigger 10 AH battery cell and we can see that the bigger cell is in fact the weaker cell, as it is rated only 10 A maximum discharge.