Battery life definition

Battery Life

In the use of lead-acid batteries, how to ensure that the battery can work normally is a very important issue. Generally speaking, the battery will not be damaged suddenly and cannot work under normal use. Therefore, when judging whether the battery is damaged, it is based on The capacity of the battery is used as the benchmark, and a complete charge and discharge test is carried out on the battery. When the capacity of the battery is below 60% of its rated capacity, it means that the battery has been seriously aged, and it can also be said that the battery has reached the end of its life.

When the battery is actually used, the battery is usually connected in series and parallel. The purpose is to increase the capacity of the battery pack. Therefore, when judging the life of the battery, a string of battery packs is used as the unit of measurement. A string of battery packs is regarded as a unit, so when setting the experimental conditions, the individual batteries of the battery pack are often regarded as the same, but there will be considerable differences in actual use, causing some batteries to age quite quickly, thus reducing the overall Therefore, the battery must be replaced before it is damaged and unusable to ensure the normal operation of the battery system.。

There are two main definitions of battery life.

Cycle life (Cycle Life):

Cycle means that the battery is used as the main power source, so the number of charging and discharging is relatively frequent, such as electric vehicles; at this time, the standard of life is to set a condition, when the capacity is repeatedly charged and discharged, the capacity drops to a certain value relative to the initial value (such as 80% or 60%), the number of cycles that can be repeatedly charged and discharged during this period.

The biggest factor affecting the cycle life of lead-acid batteries is the depth of discharge (DOD, Depth of Discharge)

, when the depth of discharge used is deeper, the number of times the battery can be recycled is less, and the relationship is shown in the figure below. For this lead-acid battery CSB (HRL12390W), when the depth of discharge is 50%, the number of cycles is about 400 to 500 times, when the depth of discharge is 100%, the number of cycles is reduced to about 200 to 300 times.

Even if the depth of discharge is deeper, the number of times the battery can be cycled is reduced, and the life expectancy is relatively reduced. However, for the safety of the battery, a capacity test has to be done. The original factory also said that the internal resistance of the battery has increased by 30% compared to when it was new. %, it may be caused by the corrosion of the plate grid inside the battery, the deterioration of the active material of the plate and the dryness of the electrolyte. So can it be boldly assumed that every time the full capacity is discharged, the internal resistance will increase by about 1~1.5%.

二.Float Life:

Floating charging refers to the state that the battery is used as a backup power source, not used normally, but only used when necessary, such as uninterruptible power system (UPS) and power failure automatic lighting, etc. At this time, the battery life is calculated by time.

The main factor affecting the life of floating charge is the charging current, because when the battery is applied in the state of floating charge, it is usually charged continuously to ensure that the battery remains fully charged, but during continuous charging, the charging current will affect the electrodes. The corrosion rate of the plate, so generally in the case of supplementing the self-discharge of the battery, the charging current should be reduced as much as possible. Therefore, the constant voltage (CV) charging method is generally used for floating charging, and the floating charging voltage is set at the charging capacity. Slightly larger than the self-discharge capacity to adjust the size of the charging current by itself, which can relatively increase the battery life.

Another factor that affects the float charge life is the temperature. The higher the temperature, the faster the corrosion rate of the electrode plate will be, resulting in faster damage to the battery. For this lead-acid battery CSB (HRL12390W) battery, the relationship between float charge life and temperature is shown in the figure below. When the battery is operated at an ambient temperature of 25°C, the battery capacity will drop to 60% after 12~13 months of use. When the ambient temperature is 30°C, the battery capacity will drop to 60% after 8 months of use. Only at 5°C, use 18 The battery capacity can only be maintained at 80% after a month.

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