After professional experiments, it has been found that the total capacity of a fully charged 18650 lithium battery will decrease by 20% after being left idle for one year; After being left idle for a year, the total capacity of lithium batteries charged to 40% only decreases by 5%. Lithium batteries that are not used for a long time can be charged up to about 50% and stored at low temperatures (such as in a refrigerator).
The battery itself will have a certain degree of self leakage, and the protective board will also have microampere level power consumption. Therefore, in long-term storage, it is necessary to regularly measure the voltage and recharge.
1. Constant current charging: This method still originates from the previous and previous circuits, but limits the high charging current. Constant current and constant voltage are actually "current and voltage limiting". This type of circuit is more popular, such as the Nanfu and Xinyu current, which do not completely cut off after being fully charged and switch to trickle float charging - now it is believed that long-term low current charging is one of the reasons for battery inflation.
2. High voltage charging: This charging method does not have a dedicated control circuit, and directly uses a 5V power head (or a diode in series to reduce voltage) to charge the battery with a protective board, completely relying on the high voltage limit of the protective board. The characteristic is that the current is high at the beginning, then gradually decreases and floats at any time.
3. Intelligent charging: This is currently considered an ideal charging management method, following the charging algorithm mentioned at the beginning of this section, integrated into a small chip IC, with simple peripheral circuits, stable and reliable, such as TP4054/4055/4056/4057, TP4002/5000, MAX1879, and so on. The main feature of this chip is that it will simultaneously monitor voltage and current when determining whether it is fully charged, and stop charging, or stop charging when the charging current is less than (usually around 50mA); Completely cut off after being fully charged, without trickle float charging, but monitor the voltage at any time. If the battery voltage drops to a certain value, start charging.
4. Constant voltage charging: This method is similar to the previous one. Constant voltage is actually a "voltage limit", setting a relatively precise high voltage and charging continuously.