Battery C rate rating explained

When it comes to batteries, 1C rate means that you are completely charging or discharging the battery in one hour. It is important to know the C rating of a battery so that you don’t charge/discharge at more current than it is made for.

  • 1C battery shouldn’t be fully discharged in less than an hour.
  • 4C battery shouldn’t be fully discharged in less than in 15 minutes.
  • 0.5C battery shouldn’t be fully discharged in less than 2 hours.

First the easy math. A 1000mAh (1Ah) battery will power something at 1C if it provides a steady 1A of current. 1C for a 2000mAh (2Ah) is when it provides 2A of current for an hour. In both cases, the battery will be fully discharged at the end of that hour.

  • Current flow divided by amp hour.
  • 1A/1Ah = 1C
  • 2A/2Ah = 1C

Slightly tougher math

If you have a 1Ah (1000mAh) battery and only use a steady 500mA of current, then the battery will take 2 hours to discharge (0.5C). And in the case of a 1Ah battery only providing 250mA of steady current, it will discharge in about 4 hours (0.25C).

  • 1Ah battery at 1 amp steady current = 1C
  • 1Ah battery at 500mA (0.5A) steady current = 0.5C
  • 1Ah battery at 250mA steady current = 0.25C
  • 1Ah battery at 2A steady current = 2C (discharged in 30 minutes)

If you want high current from a small battery, such as steady 4 amps from a 1Ah battery, then it will need to be rated for at least 4C. In that case, you can draw 4A for 15 minutes, and which point the battery will be discharged.

  • 1,000mAh battery at steady 2A = 2C and discharged in 30 minutes.
  • 1,000mAh battery at steady 4A = 4C and discharged in 15 minutes.

High C rated batteries cost a lot more than batteries with a low C rating. They are used where you want a lot of short term power in a light battery, such as those used in drones.

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