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# C-Rate of Batteries | ThinkRobotics.in

### Definition

The C rate of A battery cell represents the level of constant current charge or discharge that the cell can sustain for one hour of time.

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C rating is defined as a rating of how quickly energy is discharged from a battery.

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C-rates govern charge and discharge rates of a battery.

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C in C rate stands for the capacity of a battery usually measured in ampere-hours (Ah) indicating the amount of active material within the battery available for discharge.

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For example, a cell having a capacity of 20-ampere hours should be able to deliver 20 amperes of current for one hour or 2 amperes of current for 10 hours. The C rate may be a way of normalizing electrical current in line with a cell’s nominal capacity.

Fig 1: A typical battery with its few specification details. [9]

The capacity of A battery is often rated at 1C, meaning that a charged battery rated at 1Ah should provide 1A for one hour. The same battery discharging at 0.5C should provide 500mA for 2 hours, and at 2C it delivers 2A for a half-hour. Losses at fast discharges reduce the discharge time, and these losses also affect charge times.

A C-rate of 1C is additionally referred to as a one-hour discharge; 0.5C or C/2 is a two-hour discharge and 0.2C, or C/5 is a 5-hour discharge. Some high-performance batteries are often charged and discharged above 1C with moderate stress. Table 1 illustrates the typical times at various C-rates.

Table 1: C-rate and time of charge or discharge 1Ah Battery cell. [1]

When discharging a battery with a battery analyser capable of applying different C rates, a higher C rate will produce a lower capacity reading and vice versa. By discharging the 1Ah battery at the faster 2C-rate, or 2A, the battery should ideally deliver the full capacity in half-hour. The sum should be the same since the identical amount of energy is dispensed over a shorter time. In reality, internal losses turn some part of the energy into heat and lower the resulting capacity to about 95 per cent or less. Discharging a similar battery at 0.5C, or 500mA over 2 hours, will likely increase the capacity to above 100%.