Self-discharge of portable power stations

The consistency of self-discharge is an important factor for performance.
The SOC (State of Charge) of the battery of a power station with inconsistent self-discharge will show a significant difference after a period of storage, which can seriously affect the capacity and safety. Through our studies, we can improve the overall level of our battery packs, extend the service life and reduce the defect rate of the products.

If we store a battery or a lithium power station with a certain amount of energy at a certain temperature and maintain this condition for a period of time, it will lose some of its capacity. In short, self-discharge is a phenomenon in which the battery loses energy through side reactions.

solar-powered portable power station

The importance of self-discharge

Currently, lithium batteries are increasingly used in laptops, digital cameras and other digital devices. In addition, they also have promising prospects in vehicles, mobile base stations, portable solar power stations and some solar systems. Under these circumstances, batteries no longer appear only in isolation, as in a mobile phone, but also in series or parallel circuits.

Battery pack capacity and lifespan depend not only on each individual battery, but also highly on the consistency between batteries. Poor consistency can significantly affect battery pack performance.

The consistency of self-discharge is an important factor affecting performance. The SOC (State of Charge) of batteries with inconsistent self-discharge will have a significant difference after a certain storage period, which can greatly affect the capacity and safety. Through our research, we can improve the overall level of our battery packs, extend the service life and reduce the defect rate of products.

The influence of self-discharge

1. Self-discharge leads to a reduction in storage capacity.

Here are some typical problems caused by excessive self-discharge:

• For example, if a vehicle is parked for too long and cannot start, or a portable power station is stored outside for too long and can no longer be used.
• The battery voltage and other parameters appear normal, but the voltage suddenly dropped lower or even to zero when the battery was delivered.

2. Self-discharge caused by metal impurities will block the diaphragm pore diameter, which will even pierce the diaphragm and cause a local short circuit, which will endanger the safety of the battery.

3. Self-discharge will increase the SOC difference between batteries and reduce the capacity of the battery pack.

4. Due to the inconsistency of self-discharge, the SOC of the batteries in the battery pack is different after storage, resulting in the deterioration of the battery function. Customers often find that the performance declines after receiving the battery pack that has been stored for a period of time. When the SOC difference is about 20%, only 60% to 70% of the capacity of the combined battery pack remains.

self-discharge test

1. Self-discharge detection methods

voltage drop method
The voltage drop method uses the rate of voltage drop during storage to characterize self-discharge. This method is easy to use, but the disadvantage is that the voltage drop does not directly reflect the capacity loss. The voltage drop method is the simplest and most practical method and is widely used in current production.

capacity reduction method
This measures the percentage of capacity loss per unit of time.

self-discharge current method
Based on the relationship between capacity loss and time, the self-discharge current ISD of the battery during storage is calculated.

Calculation of Li+ mole number for side reaction consumption
Considering the influence of the electronic conductivity of the negative SEI film on the Li+ consumption rate during storage, the relationship between Li+ consumption and storage time is derived.

Important NOTE:
ALLWEI lithium portable power stations use A+ quality car lithium batteries. The self-discharge current of the battery pack is below 26µA. However, to extend the life of your portable power station, we recommend charging and discharging the device at least once every 3 months to improve battery efficiency.