 ## Explanation of lead acid battery capacity

##### Date:Apr 18, 2019

The lead acid battery size is measured in terms of battery capacity.

The battery can be used in different conditions, and the battery can discharge different capacities. In order to calibrate the capacity of the battery, the rated capacity of the battery is defined. The rated capacity is the time when the battery is manufactured. It is expressed according to the minimum amount of electricity that should be discharged under certain discharge conditions. The unit is Ah (Ah), which is the data marked on the battery.

The specified battery discharge conditions are: (1) the current discharged by the battery, generally the discharge rate; (2) the termination voltage of the discharge, the discharge current is different, and the termination discharge voltage is also different; (3) the discharge temperature, the discharge capacity of the battery at low temperature is small, and the discharge at high temperature The capacity is large, and the discharge temperature is specified in order to unify the discharge capacity.

The discharge rate is the magnitude of the discharge current of the battery, which is the time rate and current rate.

The discharge time rate refers to the length of time that the discharge is terminated to a termination voltage under a certain discharge condition. According to the IEC standard, the discharge rate is 20 hours (20Hr, the most common one, which is generally indicated on the battery), 10 hour rate (10Hr), 5 hour rate (5Hr), 3 hour rate (3Hr). , 2 hour rate (2Hr), 1 hour rate (1Hr), 0.5 hour rate (0.5Hr), and the like.

As the battery is discharged, the terminal voltage of the battery will gradually decrease. The lowest voltage that is discharged at 25 ° C until it can be repeatedly charged again is called the discharge end voltage (OCV). The discharge rate is different and the discharge termination voltage is also different. Generally, the termination voltage at a 10-hour rate is mostly 1.8V/single (10V battery is 10.8V), and the termination voltage at a 20-hour rate is generally 1.75V/single (10.5V for a 12V battery). Below this voltage, although a little more power can be discharged (that is, the electricity has been discharged, it is a deep discharge), but the capacity for recharging is easy to fall, so do not discharge below this voltage unless special circumstances.

The rated capacity of the battery is expressed by C. The battery capacity obtained by different discharge rates will be different. For example, the current value represented by the discharge current of 10 hours is: I10=C10/10=0.1C10, discharge current of 2 hours discharge rate The current value is: I2=C2/2=0.5C2, and the discharge current of the 1-hour discharge rate indicates the current value: I1=C1/1=1C1.

The discharge current of the battery is different, and the capacity that can be discharged is also different. The larger the discharge current, the smaller the amount of electricity that can be discharged. For example, the electric current commonly used in electric bicycles is 5A, and the battery using the nominal 10Ah is a 2-hour rate discharge. If a 10-hour rate discharge is used, it can reach 12Ah. Thus, if the battery is nominally 2 hours, it should be 10 Ah, if it is 10 Ah according to the 10 hour rate. Therefore, looking at the capacity of the battery depends not only on the capacity of the battery, but also on the discharge rate of the battery. The battery of an electric bicycle is often nominally 10Ah (2Hr), and the same battery can also be labeled 12Ah (10Hr) and 14Ah (20Hr). Another example. The 14Ah (2Hr) battery can also be labeled 17Ah (10Hr). Some batteries have a capacity of 20 hours, and the battery capacity is nominally large, but there is no significant change in battery capacity.

In addition, the larger the discharge current, the shorter the life of the battery; the deeper the discharge depth, the shorter the life of the battery.

Lead-acid batteries can cope with short-time high-current discharges, and the depth of discharge is not deep. Small current discharge, even if the depth of discharge is slightly deeper, the life of the battery is not greatly affected. Most afraid of continuous high current discharge and deep discharge. Therefore, the battery with the nominal 17Ah is used for electric friction, and the discharge current is generally 10A to 17A at a speed of 35 kilometers per hour, that is, it is discharged at about 1C, so the discharge current is relatively large. Such a battery not only has a reduced capacity, but also has a relatively short service life. And most of the electric motorcycle users' continuation ability requirements are also longer than electric bicycles, so the electric discharge depth is relatively deeper. And the speed of the electric motorcycle is relatively faster, and the braking and starting acceleration are more frequent, and the capacity of the battery is more consumed. Therefore, the actual service life of frequently used electric motorcycle batteries is generally 3 to 6 months, and will not be very long.