Many lithium polymer batteries come with a C on the package, with a number in front of the C. So what exactly does this C Rating mean?
What is C Rating?
The C rating of a lithium polymer battery refers to the maximum discharge rate allowed for the battery relative to its capacity.
For example, if a cell has a capacity of 2400 mAh and its C rating is 20C, which means that the cell is capable of discharging at a rate of 20 x 2.4 = 48 amps.
If a battery has a capacity of 4000 mAh and its C rating is 10C, then:
10 x 4 = 40 amps.
Now it makes sense.
The higher the C rating, the more energy it can release in a short period of time. And the more energy released, the faster your battery will run out of power.
If you have a 10Ah battery – and you discharge it at 20C – then you will be drawing 200 amps – and it will be fully discharged in 3 minutes.
The main difference between the different C batteries is that the higher category batteries tolerate a lower voltage drop under load. This ability to maintain a higher and more stable voltage is often the reason for the high performance we like.
The C rating also allows the user to easily calculate the maximum current that can be safely delivered from a LiPo battery without damaging it.
The charge/discharge efficiency of Li-polymer batteries is also related to the C-rate. At 0.2C, the charge/discharge efficiency of Li-polymer batteries should be 99.8%.
Charge/discharge efficiency = Discharge capacity/Charge capacity x 100%.
Rated capacity: the rated capacity is the electrical energy that can be released by a full charge and continuous discharge of the battery under no-load conditions to the disconnect voltage. It is usually expressed by the symbol mAh or Ah (1000mAh=1Ah).
However, if the battery is used with a connected load and after prolonged use, the amount of energy discharged by the battery decreases. Since charging and discharging take place under specific C-rate conditions, the capacity of the battery is directly related to this rate. The rated capacity of a battery under normal conditions is the capacity of a battery tested at 0.2C.
The higher the C-rate, the lower the discharge rate of the battery.
Charge capacity = charge current x charge time;
discharge capacity = discharge current x discharge time.
Generally speaking, a discharge current of 0.2C can achieve a discharge rate of 95%~100%, while a discharge current of 1C can only achieve a discharge rate of about 90%, because the charge is affected by the characteristics of the raw material of the battery itself, so it must be charged part of the time accordingly.
When shopping for the right lithium polymer battery for your FPV drone or other equipment such as RC cars, the C rating is an important factor that must be considered.
As mentioned above, C-rating is an important consideration when you choose a LiPo battery.
However, there are many LiPo manufacturers who deliberately exaggerate the C-rating of their LiPo batteries to deceive consumers and increase their battery sales. Therefore, you should not blindly trust the C-rating and ignore other aspects.
How to calculate current with C Rating?
The formula for calculating the current is simple.
Current = C rating x Capacity
Let’s look at the example of a 3S 2000mAh 20C LiPo battery, the maximum safe current consumption is
2000mAh (2Ah) x 20C = 40A
Let’s look at another example, a 5000mAh LiPo battery with a C rating of 10C, the same.
5000mAh (5Ah) x 10C = 50A
It’s not that difficult, right?
So, if the output current exceeds the maximum safe current of the battery, then this will cause irreversible damage to the battery and thus reduce the battery life.
Factors that influence C Rating
Basically, the internal resistance of the battery and the merit of the connector are the main factors affecting the C rating. The internal resistance of the battery limits the maximum current output of a LiPo battery (usually for safety reasons). Batteries with high internal resistance usually do not have a high C rating.
In general, the lower the average discharge and charge rate is kept, the longer the battery life will be, which is why slow charging is much better than fast charging if you can.
A higher C rating means the battery can withstand high power output (and fast charging), but that doesn’t mean it’s good for the long-term life of the battery.
Is higher C Rating better?
In the vast majority of cases, higher C rating batteries are better because they provide greater and more stable energy, which means that it allows your RC device to show more powerful performance.
However, it is also important to note that you should use high C rating batteries reasonably according to your device, otherwise there will be safety issues.