Meaning of battery capacity in C100, C20 or C5

Technical standards such as IEC 60896-11 or din 40736-1, among others, are used to certify the capacity of a battery and to be able to compare the values ​​provided by different manufacturers.

Capacity in C100: c100 battery meaning

The capacity in Ah of a battery expressed in C100 means that these amperes / hours can be extracted from the battery as long as the  discharge rate is such that it completely discharges in  100 hours.

For example, the  Hoppecke 6 OPzS 600 stationary battery  according to the data sheet provided by the manufacturer has:

C100: 900 Ah
C10: 686 Ah
C5: 590 Ah
C3: 510 Ah
C1: 353 Ah

Therefore, in C100 with 900Ah,  if we apply a constant consumption with a current rate of 9A for 100h, we will have that the battery will be able to supply 900Ah from full load to depleting 100% of the battery capacity.

• If the battery is 12V, the consumption would be 108W during 100h. (Since 9Ah x 12V = 108Wh). Total energy (in 100h) = 10.8kWh
• If the battery is 24V, the consumption would be 216W during 100h. (Since 9Ah x 24V = 216Wh). Total energy (in 100h) = 21.6kWh

If the same battery is discharged at a rate such that it implies a complete discharge in 10 hours (C10), the amperes / hour that we can extract will be much lower than the value of C100.

In C10 the battery has 686Ah.  Which means that if the consumption has a current rate of 68.6A we would discharge the entire battery in just 10h.

• If the battery is 12V, the consumption would be 823.2W for 10h. (Since 68.6Ah x 12V = 823.2Wh). Total energy (in 10h) = 8.23kWh
• If the battery is 24V, the consumption would be 1646.4W for 10 hours. (Since 68.6Ah x 24V = 1646.4Wh). Total energy (in 10h) = 16.4kWh

In C5 the battery has 590Ah  therefore with a discharge rate of 118A we would drain the battery in 5h.

• If the battery is 12V, the consumption would be 1416W for 5h. (Since 118Ah x 12V = 1416Wh). Total energy (in 5h) = 7.08kWh
• If the battery is 24V, the consumption would be 2832W for 5 hours. (Since 118Ah x 24V = 2832Wh). Total energy (in 5h) = 14.1kWh

We see that the battery capacity is not proportional to consumption and that the higher the discharge current rate, the lower the capacity in Ah provided by the battery.

This fact is due to the increase in the internal current flow of the battery. The higher the current, the faster the reduction chemical reaction, producing greater sulfation and covering the internal plates of the battery, reducing its porosity and the ability to extract energy from the chemical reaction.

• To remember we can use the example of a broker. An expert runner running at a moderate speed is capable of running for 5 hours without a break. If this same runner exprints he will only be able to run for 10 minutes.

The manufacturer uses for the name the nominal capacity of the battery in C10  and therefore the name is 6 OPzS 600, while for applications of solar installations we are more interested in knowing the capacity in C100 since the batteries in this application will be more close to this discharge rate.

• There will be times during the day when the discharge rate of our battery will be around C10 when we connect a high consumption such as an oven and times when this rate will be closer to a C200 where the consumption is a light bulb. But for practical purposes we consider that the average will be around the C100 as long as the battery is well dimensioned.
• For applications such as golf carts or wheelbarrows, traction or semi-traction batteries expressed in C20 are usually used since the battery will discharge in 1 day (approx. 20 hours) and the C20 value is used to perform the design calculations.

Tip:  Take a good look when you go to buy a solar battery in which unit the capacity is expressed in order to be able to compare some prices with others.