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Battery C Rating Explained and Demystified
This entry was posted on January 21, 2016.
Batteries are a bit of a mystery to people. They are not quite an electronic, so you dont have to program the time on them. However, they all have strange markingsĀ on them that battery manufactures expect you to understand. For instance, C Rating is found on most Li-PO battery packs. Typically it will look will something like 20C or 20C – 30C. So what does it mean? Watch the video below or read on for the explanation.
C Rating Background
C Rate is derived from Coulomb’s Law developed by French physicist Charles Augustin de Coulomb. The c-rate is the governing measurement of what current a battery is charged or discharged at. For example, the posted mAh of the battery is the 1C rating. If a battery is labeled 2000mAh, then its 1C rating is 2000mAh.
To make this simple, the battery should provide 1C current for one hour. In our example above that would be 2000mAh or 2A of current for one hour. The same applies for a 0.5C rating. Again using the 2000mAh battery, it would deliver 1000mAh or 1A of current for two hours.
Battery C Rating Examples
The formulas for the example are simple. If for any reason I have not made it clear, comment for further explanation. The following examples are based on the first line in the table. 1600mAh battery with a 10C rating.
Continuous Discharge
(mAh / 1000) x C Rate = Continuous Discharge Amperage
(1600 / 1000) x 10 = 16A
Run Time for Safe Continuous Discharge
60mins / C-Rate = Run Time
60mins / 10C = Discharge 16A for 6mins
Use the formulas above, the tableĀ has examples of common amperage batteries and C Rates found on them. They are not for literal products and are only used as hypothetical examples.
Amperage (mAh)
C-Rate
Cont. Discharge (A)
Run Time (Mins)
1600
10C
16A
6
2000
20C – 40C
40A – 80A
Ā 3 / 1.5
2500
25C
62.5A
2.4
3500
30C
105A
2
5000
20C
100A
3
As you you can see in the chart, the 3500mAh battery will produce a higher continuous discharge than the 5000mAh battery. However, the 5000mAh battery will deliver its current 33% longer than the 3500mah battery. So which result is more important to your application. Longer run time or higher continuous amperage discharge. If your battery is in an airsoft gun your probably looking for run time. If your using an e-cigaretteĀ batteryĀ then your probably looking for a higher continuos amperage.
If a manufacturer has a specification such as 40C for a battery, there needs to be a way to verify that specification. A test method. Otherwise it is just marketing hype. Meaningless.
Mike
I agree and to provide those ratings the batteries undergo tests that give them the ratings. These tests are generally provided on a specification sheet that you can request from the manufacture if you want to see them.
Why does c rating even exist? Why not just list the amps a battery can supply and be charged at. Why throw another math problem in the mix?
Just curious where it started being used for lipo packs and why we don't just use amps.
The C rating is used because not everyone is using the battery in the same way. Drawing amperage from the battery at different rates give you different results. Using the C rate you can mathematically determine how long the battery will sustain what you are drawing from the battery. It also is a gauge for what the largest draw from the battery is possible without damaging the battery