18650 battery flat top

　　Someone has done a special experiment, and the total capacity of a fully charged 18650 lithium battery will drop by 20% after one year of standing; while the total capacity of a lithium battery charged to 40% will only drop by 5% after one year of standing. Lithium batteries that have not been used for a long time can be charged to about 50%, and stored at low temperature (such as a refrigerator freezer).

　　The battery itself will have a certain self-leakage, and the protection board will also consume power at the microampere level, so in long-term storage, it is necessary to measure the voltage regularly and recharge it.

　　1. Constant current charging: This method is still derived from the previous and previous circuits, but it limits the very high charging current. Constant current and constant voltage are actually "current limiting and voltage limiting". This kind of circuit is more popular, such as Nanfu, Hexinyu and others don’t cut off completely after being fully charged, but instead use trickle floating charge – it is now believed that long-term low-current charging is one of the reasons for the battery’s flatulence.

　　2. High-voltage charging: This charging method does not have a special control circuit, and directly uses a 5V power source (or a series of diodes to step down) to charge the battery with a protection board, completely depending on the high-voltage limit of the protection board. The characteristic is that the current is very large at the beginning, and then gradually decreases, and it can be floated at any time.

　　3. Intelligent charging: This is an ideal charging management method now. It follows the charging algorithm mentioned at the beginning of this section and is integrated in a small chip IC. The peripheral circuit is simple, stable and reliable, such as TP4054/4055/4056 /4057, TP4002/5000, MAX1879, etc. The main feature of this chip is that it will monitor the voltage and current at the same time when judging whether it is full, stop charging, or the charging current is less than (usually about 50mA) stop charging; completely cut off after full, there is no trickle floating charge, but it can be monitored at any time Voltage, if the battery voltage drops to a certain value and then start charging.

　　4. Constant voltage charging: This method is similar to the previous one. Constant voltage is actually "limited voltage". Set a relatively accurate high voltage, and then charge to that voltage. , if this kind of charger makes the cut-off voltage very accurate, it will be safe if it is too low. If it is too high, you have to rely on the protection board. It is common in the current mobile phone universal charging and flashlight direct charging. This kind of charger costs less than one yuan, and it is all made of inferior parts.