In general, lithium batteries have high-current over-discharge protection circuits.
If the battery is discharged several times and is not charged immediately (the battery recovery capacity is low), the battery voltage is too low, the protection circuit is in a cutoff state, and the loading process cannot be completed.
Solution: You can open the battery case, directly connect the two poles of the charger to the two poles of the battery through the protection circuit (pay attention to the polarity, you can use a multimeter to test the positive and negative poles first), charge for a few minutes and the battery voltage will increase, the protection circuit can be opened.