C-Rating Explained: Continuous vs. Burst Current
Matching your battery's power output to your motor's demand.
When looking at battery specs, you'll often see a 'C' number (like 10C or 25C). For beginners, this is the most confusing part of battery math. But the C-rating is actually a simple multiplier that tells you how much current the battery can provide relative to its capacity. Getting this wrong means your battery will sag, overheat, and potentially catch fire under heavy load.
The C-Rating Formula
The 'C' stands for Capacity. 1C is the current required to discharge a battery in exactly one hour. For a 3Ah (3000mAh) battery, 1C is 3 Amps. If that battery is rated for 10C, it can provide 30 Amps (3Ah x 10). A 20C rating would mean 60 Amps. It's a way to standardize power output across different battery sizes.
Continuous vs. Burst Rating
Most quality batteries provide two ratings. The 'Continuous' rating is what the battery can provide safely until it is empty. The 'Burst' or 'Peak' rating (usually much higher) is what it can provide for a few seconds (e.g., during hard acceleration). Never design your system based on the burst rating; it is only a safety buffer for short-term spikes.
The Price of High C-Ratings
High C-rate cells (like those used in racing drones or high-performance EVs) have thinner internal components to reduce resistance. This allows for massive power, but it comes at a cost: lower energy density (shorter range) and fewer total charge cycles. For long-distance commuting, a 'medium' C-rate cell (like the LG MJ1 or Sanyo GA) is often a better choice for longevity.
Sag: The Voltage Drop Under Load
When you pull high current from a battery, the voltage 'sags' due to internal resistance. If your battery is rated for 10A and you pull 10A, your voltage might drop from 42V to 38V instantly. This makes your motor feel weak. By using a higher C-rated battery or adding more cells in parallel, you reduce the per-cell load, minimizing sag and keeping your performance snappy.
FAQ
Can I charge my battery at a high C-rating?
Usually no. Discharge C-ratings are much higher than charge ratings. Most standard lithium cells should be charged at 0.5C or 1C. Charging too fast causes lithium plating and will permanently damage the battery.
Is a 100C battery better than a 10C battery?
Only if you need the power. A 100C battery is optimized for extreme bursts but will have less total energy storage (Wh) and a shorter lifespan than a 10C battery of the same weight.
How do I find my cell's true C-rating?
Always check the official manufacturer's datasheet (Samsung, Sony, Panasonic, etc.). Marketing labels on generic blue-wrapped batteries are often wildly exaggerated and should not be trusted.