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I. Main Factors Affecting the Self-Discharge Rate of Lithium-Ion Batteries:

• The self-discharge rate of battery cells and the storage temperature of batteries;

• The consumption current generated by the battery management circuit within the battery pack;

• The consumption current generated by the static current of the equipment when the battery is installed inside the host;

• The consumption current generated by the static current of the charging circuit when the battery is connected to the charger;

• The capacity of the battery, including the number of battery cells connected in parallel within the battery pack.

II. What is the Self-Discharge of Lithium-Ion Batteries?
Due to the spontaneous occurrence of physical and chemical discharges inside lithium-ion batteries, self-discharge will occur slowly within the battery cells, resulting in the loss of electric charge and the loss of chemical energy. Generally, the self-discharge rate of lithium-ion batteries is 0.5% - 3% per month. The storage temperature of the battery has the greatest impact on the self-discharge rate. Higher temperatures will intensify the internal chemical reactions of the battery, leading to more self-discharge. Therefore, the storage environment of the battery has a significant impact on the life of the battery.

III. The Self-Consumption of the Battery Management System (BMS)
Inside a smart battery, in addition to the battery cells, a battery management circuit (BMS) is required to monitor the battery current, voltage, and temperature in real-time, providing safety protection and battery capacity calculation for the battery. Besides the self-discharge of the battery cells, these electronic components will also cause additional current consumption to the battery product.

The battery management system is 精心 designed to minimize current consumption and has different working modes with different current consumptions in different modes. The standard smart batteries of JUDA usually have the following working modes:

• Normal Mode: < 500 μA (battery charging/discharging state or communication state)

• Sleep Mode: < 200 μA (automatically entered when there is no charging/discharging current and no communication conditions for the battery, lasting for more than 20 seconds)

• Shutdown Mode: < 10 μA (actively entered when the battery cell voltage is lower than 2.2 V or when the host sends an instruction)

Through the above data, the theoretically consumed battery capacity of the battery management system circuit during one-month static storage can be calculated as follows: 0.2 mA * 24 h * 30 days = 144 mAh. (200 μA = 0.2 mA)

Assuming that the battery is stored under the best conditions, the performance reference of the BMS self-consumption of the lithium-ion battery pack plus the self-discharge amount of the battery cells (at 1%/month) is as follows:
From the above figure, we can draw the following conclusions:

• The battery capacity has a direct relationship with the storage shelf life of the battery. Batteries with a smaller capacity can be stored for a shorter period of time, while batteries with a larger capacity or more parallel-connected battery packs can be stored safely for a longer period of time.

• The state of battery charge has a direct relationship with the storage shelf life of the battery. Before long-term storage, the battery should be recharged to more than 30%.

• The battery should be inspected every six months. If the capacity is lower than 30%, it should be recharged to more than 30%.

IV. Shutdown Mode
The battery management system BMS has a shutdown mode to minimize current consumption. When the voltage of the battery cell drops below 2.2 V, the BMS will enter the shutdown mode and turn off the battery output. At this time, the self-consumption of the BMS will be reduced to about 1 μA, avoiding permanent failure of the battery due to severe under-voltage. This mode needs to be activated by charging.

If the customer needs to store the battery for a long time or transport it by sea for a long period, the host can actively send an instruction to make the battery enter the shutdown mode, which can minimize the self-consumption of the battery and extend the storage time of the battery. Shutdown Instruction: Send the 0x0010 instruction twice consecutively within 2 seconds to the battery address 0X16.

V. Transportation Safety
Since 2016, IATA/UN/DOT has restricted the charging state of batteries to be less than 30%. We must follow these requirements, so all our batteries are shipped with a charge level of less than 30%. It is recommended to recharge the battery in time after receiving it. If you don't use it for a long time after receiving it, the battery charge may drop to 0, and if it is not charged six months after leaving the factory, there is a risk of permanent failure of the battery.

VI. Storage at Full Charge
Considering the self-consumption of the battery, some customers may store the battery at full charge for the sake of maximum storage time. However, lithium-ion batteries should not be stored at 100% charge. If stored continuously at 100% charge, lithium-ion batteries will lose a certain amount of capacity. This is very common in UPS applications and laptop computers. When continuously maintained at full charge, lithium-ion batteries will lose 5% - 10% of their original capacity. We recommend that the long-term storage charge level of the battery be around 50%.

VII. Calendar Life
Even if the battery is not charged or discharged, due to the aging of the chemicals inside the battery cells, there will be certain losses during long-term storage. Our empirical value is 5% per year.
If used normally, the empirical value is that the battery capacity loss is about 5% for every 100 cycles.

VIII. Summary
There are many other factors that affect the actual shelf life of lithium-ion batteries. For the general maintenance methods of lithium-ion batteries, we recommend:

• Inspect the inventory batteries once every four months; especially those that have been installed inside the equipment and have not been used for a long time and cannot be charged.

• The storage time of lithium-ion batteries under low SOC conditions should not exceed six months.

• The storage temperature has a great impact on the battery. Store the battery at room temperature or slightly below room temperature (ideally 10 - 20 °C).

• When the battery needs to be transported, keep the charge state at less than 30% to comply with regulatory requirements.

• Our products stipulate that the capacity should be inspected every six months and charged in time if necessary.

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