Generally, a 3.7V lithium battery needs to have a "protection circuit board" for overcharging and overdischarging. If the battery does not have a protection circuit board, it can only be charged with a voltage of about 4.2V, because the ideal full charge voltage of a lithium battery is 4.2V. If the voltage is exceed 4.2V, the battery may is damaged, it is necessary to monitor the condition of the battery at the same time when charging with this method.
With the protection circuit board, you can use 5V to charge (4.8V to 5.2V can be used), the USB 5V charger of the computer or the 5V charger of the mobile phone can be used.
3.7V battery, charge cut-off voltage 4.2V, discharge cut-off voltage is 3.0V. Therefore, when the open circuit voltage of the battery is lower than 3.6V, it should be able to charge. It is best to use 4.2V constant voltage charging mode, you don't need to pay attention to the charging time. Charging with 5V is prone to danger of overcharging.
The usual lithium battery cell is 3.7V, the voltage is 4.2V when fully charged, and the nominal voltage after series connection is 7.4V, 11.1V, 14.8V...The corresponding full voltage (that is, the charger is no-load The output voltage) is 8.4V, 12.6V, 16.8V...
How to charge the 3.7V lithium battery?
Lithium batteries are most afraid of overcharging and overdischarging. Its charging needs to be divided into four processes: activation charging, constant current charging, constant voltage charging and trickle charging.
Activation charging: When the voltage is too low, a smaller current is required to activate and charge the lithium battery.
Constant current charging: After the voltage rises, it can be changed to constant current fast charging.
Constant voltage charging: When the voltage rises to 4.2V, it needs to be changed to 4.2V constant voltage charging, and the charging current gradually decreases.
Trickle charge: After fully charged, change to trickle charge to maintain the full charge of the lithium battery.