3.7V battery, the charging cutoff voltage is 4.2V and the discharge cutoff voltage is 3.0V. Therefore, when the battery open circuit voltage is lower at 3.6V it should be able to charge. It is best to use 4.2V constant voltage charging mode, so you don't need to pay attention to the charging time. Charging with 5 V is subject to overcharging and is dangerous.
3.7V 18650 lithium batteries can be directly connected in parallel, which will not damage the battery life, and can be directly charged in parallel, but the time of charge takes slightly longer.
After 18650 lithium batteries are connected in parallel, when discharging, the largest one will be removed. The higher the voltage, the faster the voltage will drop, and eventually they will be the same. level. When charging, there will be "a hole in thebig", and the charging voltage will increase slowly and the voltage will decrease finally, it will be at the same level until it is fully charged.