How to Calculate the “C” Value You Need for Your Battery

The “C” value of a drone’s battery refers to its capacity. Specifically, a battery’s capacity to discharge a certain amount of current (amps).

If you get a battery whose “C” value is too low for your drone then you can end up damaging your battery. Damaging, as in, shortening its lifespan, melting its components, or setting it on fire.

If you get a battery whose “C” value is higher than what your drone needs then the worst thing that can happen is that you paid for more than what you needed. Your drone and battery won’t be negatively affected.

ESCs Essentially Determine the “C” Value You Need

In nearly all cases your drone’s motors are by far going to be the component that requires the most power. Therefore, if you tally up how much power each motor needs then you’ll have a good idea of the minimum “C” value your battery needs to have.

Since ESCs control your drone’s motors (and you will have already determined how much power your ESCs need to be based on your motor specifications), you can simply add the power requirements for your ESCs to come to a minimum “C” value for your battery.

So for example, say you have a quadcopter, and each motor is controlled by a 30 amp ESC. Leaving aside safety margins and additional sources of amp draws, this means your battery’s “C” rating needs to handle around 120 amps (30 amps x 4 ESCs = 120 amps).

Here’s how the “C” number is technically calculated:

• First determine how much current your battery is designed to max discharge in one hour. For example: a 1,000 mAh battery is designed to discharge 1 amp (1,000 mA) over one hour.
• The “C” value is the multiplier you put in front of this. So if this 1,000 mAh hour battery was rated at 60C, that would mean it can safety discharge bursts of 60 amps of current.
• But in the quadcopter example above you need a “C” rating that can handle 120 amps. For this particular battery, that means you’d need to double the 60C to 120C. Since batteries are typically rated somewhere between 20C and 100C, what you’ll need to do in this case is find a battery that has a higher mAh rating.

So in the quest to get a battery with a proper “C” rating for your 120-amp quadcopter, you consider a 2,000 mAh battery. Here’s how you calculate the “C” value you’d need for this battery:

• First determine how much current your battery is designed to max discharge in one hour. A 2,000 mAh battery is designed to discharge 2 amps (2,000 mA) over one hour.
• You know that the “C” value is the multiplier you put in front of this 2 amps. You know your drone’s ESCs need a combined total of 120 amps. So 2 multiplied by what is 120? Answer: 60. So if you could find a 2,000 mAh battery with a 60C rating, this would fit your 120-amp quadcopter.

Now, this is a minimum for the sake of calculating. To be minimally safe, add an extra 10 percent to the “C” value you determine you need for your battery. So in the example above, instead of getting a battery that can support 120 amps, get one that can support 132 amps.

And technically ESCs aren’t the only draws of power from your battery, though they are by far typically the most energy-intensive.

For an average consumer quadcopter, you can expect the combined energy draw of four engines/ESCs to be anywhere from 40 amps (very small quadcopters) to 120 amps (average quadcopter).

If you pack a ton of accessories on one of those you might generate an additional energy draw that combined is 5 amps. You’re not going to pack a ton of accessories onto a teeny quadcopter, so let’s go with the 120-amp figure for an average quadcopter. Maxed out with accessories, that brings the drone’s total amp demand to 125 amps, as opposed to 120 amps when you only factor in the ESCs/motors.

Here are some examples of extra accessories and their amperage demands:

• FPV video transmitter: 1 amp
• Advanced flight computer (eg: Raspberry Pi): 1.5 amps
• LEDs: 1 amp
• Servo: 0.5 amps
• Telemetry: 0.2 amps
• LiDAR: 0.2 amps
• GPS: 0.1 amps

Continuous Current Draw Versus Burst/Peak Current Draw

When not otherwise specified (as is typically the case), a battery’s “C” rating and an ESCs amp rating refer to power demands during full-throttle. This is also considered burst current or peak current. Operating your drone under normal conditions (10-second bursts of full-throttle interspersed throughout your drone’s flight) based on the calculations discussed thus far on this page should be completely fine.

But for extra detail, some batteries may have a continuous discharge “C” rating listed alongside a burst/peak discharge “C” rating. Likewise, some ESCs may have a continuous current rating listed alongside a burst/peak current rating.

As a general rule, the continuous discharge ratings are about half the value of the burst-peak ratings.