Under normal circumstances, 3.7v lithium batteries need a “protection plate” for overcharge and overdischarge. If the battery does not have a protection plate, only a charging voltage of about 4.2v is used. Therefore, the ideal full charging voltage of lithium batteries is 4.2v, and the voltage exceeds 4.2 v may damage the battery, charging in this way also needs to monitor the condition of the battery at all times. You can use 5v if there is a protective plate (4.8 to 5.2 can be used), the 5v USB of the computer or the 5v battery charger of the mobile phone can be used.
For a 3.7V battery, the charge cut-off voltage is 4.2V and the discharge cut-off voltage is 3.0V. So when the battery open circuit voltage is less than 3.6V, it should be ready to charge. It is best to use 4.2V constant voltage charging mode, you can not pay attention to the charging time. Charging with 5V is easy to overcharge and cause danger.
1. Float charge. Refers to the line charging while working. This method is usually used in backup power locations. If it is less than 12 volts, it cannot be charged, and if it is too high, it will endanger the work of the power supply circuit. Therefore, when the float is working, the voltage is 13.8 volts.
2. Cycle charging. For the battery to fully charge the recovery capacity, when fully charged, do not disconnect the battery charger for measurement, usually around 14.5 volts, and the highest does not exceed 14.9 volts. 24 hours after disconnecting the battery charger, typically around 13 volts to 13.5 volts. About 12.8 to 12.9 volts after a week. The specific voltage value of different batteries is different.