Generally, a 3.7V lithium battery needs an overcharge and overdischarge protection circuit board. If the battery does not have a protection board, it can only be charged with a voltage of about 4.2V, because the ideal full charge voltage of the lithium battery is 4.2V, and the voltage may be damaged if it exceeds 4.2V. The battery is charged by this method and the battery status needs to be monitored at all times.

Lithium battery  with protection circuit board can be charged with 5V voltage(4.8V to 5.2V can be used).

charge the 3.7V lithium battery


For 3.7V lithium batteries, the charge cut-off voltage is 4.2V and the discharge cut-off voltage is 3.0V. Therefore, when the open circuit voltage of the battery is lower than 3.6V, it can be charged. It is best to use 4.2V constant voltage charging mode, you can not pay attention to the charging time. Charging with 5V voltage is easy to cause danger of overcharging.

The typical lithium battery cell is 3.7V, the voltage when fully charged is 4.2V, the nominal voltage after series connection is only 7.4V, 11.1V, 14.8V ... The corresponding full voltage (that is, the charger no-load output voltage ) Is 8.4V, 12.6V, 16.8V ...


Why is the output of the 3.7V lithium battery charger 5V?


The voltage of the lithium battery is 3.7V, and it is 4.2V when fully charged. The charging voltage must be higher than 4.2V to be fully charged. The normal charger has a dedicated IC to control the charging of the lithium battery. This 5V voltage is only supplied to this IC and related control circuits. The charging circuit controls the charging, not the 5V voltage directly to charging lithium batteries.

Lithium battery charging is relatively demanding. Generally, constant current charging is used to let the battery reach a certain voltage value, and then switch to constant voltage power supply. The constant current charging speed is relatively fast, but the lithium battery cannot be overvoltage, otherwise it will be damaged or even explode. Therefore, when it is close to the highest voltage, it will switch to constant voltage power supply, slowly charge upwards, and charge to 4.2 volts before stopping charging.