What is the C-rate about the battery?

[zhangjuan]

when we say that a battery receives a charge current of one ampere (1A) passes one coulomb (1C) of charge every second, what does it mean? How to understand the C-rate about the battery?

 

[A123rc]

In the late 1700s, Charles-Augustin de Coulomb ruled that a battery that receives a charge current of one ampere (1A) passes one coulomb (1C) of charge every second. In 10 seconds, 10 coulombs pass into the battery, and so on. On discharge, the process reverses. Today, the battery industry uses C-rate to scale the charge and discharge current of a battery.

Most portable batteries are rated at 1C, meaning that a 1,000mAh battery that is discharged at 1C rate should under ideal conditions provide a current of 1,000mA for one hour. The same battery discharging at 0.5C would provide 500mA for two hours, and at 2C, the 1,000mAh battery would deliver 2,000mA for 30 minutes. 1C is also known as a one-hour discharge; a 0.5C is a two-hour, and a 2C is a half-hour discharge.

To obtain a reasonably good capacity reading, manufacturers commonly rate lead acid at 0.05C, or a 20-hour discharge. Even at this slow discharge rate, the battery seldom attains a 100 percent capacity. Manufacturers provide capacity offsets to adjust for the discrepancies in capacity if discharged at a higher C?rate than specified. Figure 1 illustrates the discharge times of a lead acid battery at various loads as expressed in C-rate.
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