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Whats is the discharge rate of a Battery?

When we buy a battery or look at the data sheet of a battery, it is always accompanied by a letter  C  and a number ( C1, C10, C100 …) The charge and discharge rates of a battery are governed by the  C rates . A contiuacion analizaremos what does c100 mean on a battery.

The capacity of a battery is usually rated at  1C, which means that a fully charged battery rated at 1Ah should provide 1A for one hour. So if this same battery discharged at 0.5C then it should deliver 500mA for two hours, and if discharged at 2C then the battery should deliver 2A for 30 minutes. 


It is important to note that these values ​​provided by the manufacturer for a charge or discharge are based on measurements under ideal conditions, that is, for example, when the battery is subjected to ideal temperatures of 25ºC.

It is important to note how temperature affects battery life. Below is a standard example table showing the life of AGM/GEL batteries as a function of operating temperature:

Whats is the discharge rate of a Bsttery?

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As can be seen, the duration is exponential  or practically exponential as a  function of said temperature. It is also important to see how the same temperature affects the capacity of said battery. In the following table it can be seen how the capacity decreases greatly at low temperature:

Whats is the discharge rate of a Bsttery?

Regarding the discharge rate, a C rate of 1C is also known 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 can charge and discharge above 1 C at moderate voltage. Typical times based on various C-rates are shown below:

Battery capacity, or the amount of energy a battery can hold, can be measured with a battery analyzer. The analyzer discharges the battery at a calibrated current while measuring the time until the discharge end voltage is reached. For many typical lead-acid batteries, the typical end-of-discharge voltage value is 1.75V/cell. For Nickel-Cadmium batteries (NiCd/NiMH) the typical value drops to 1.0V/cell and for the most common Lithium (Li-ion) batteries the typical value goes up to 3.0V/cell.

If a 1Ah battery provides 1A for one hour, an analyzer displaying results in percentage will show 100%. Therefore, if the discharge lasts 30 minutes before reaching the final discharge voltage, the battery has a capacity of 50%. A new battery can sometimes produce more than 100% of its capacity.

 It is also important to note that in a discharge, internal losses convert part of the energy that is charged or discharged into heat and reduce the resulting capacity. That is why it is also very important to keep in mind that when we discharge a battery at a rate higher than the rate given by the manufacturer, it will not be able to deliver the nominal capacity, but rather something less. This value will depend on the download speed.

To get a reasonably good capacity reading, manufacturers generally rate lead-acid batteries at a very low level of 0.05 C, or a 20-hour discharge. Even at this slow rate of discharge, batteries rarely reach 100% capacity. Manufacturers provide capacity compensations to adjust for discrepancies if they are discharged at a higher C rate than specified. Below are the discharge times for a lead-acid battery according to various consumptions expressed in rate C:

C1, C10, C100

The smallest batteries have a discharge rate of 1C. Due to slow behavior, therefore, lead acid is usually classified at 0.2C (5h) and 0.05C (20h). While lead-nickel batteries can discharge at a high rate, the protection circuitry in Lithium batteries (usually seen as BMS) prevents the cell from discharging above 1C.


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