It can be a cell charge requested by the lithium battery (balancing charge or trickle charge). It can occur "randomly" and sometimes for several days, mainly when the battery has not been fully charged for some time. You will not be able to use the batteries during this period. It can also appear as a "micro" charge at night. 

It is the lithium battery that decides when it is necessary to rebalance the cells or calibrate the coulomb counter. 

You should see on OS ONE, in the tab "Settings" section "Battery" a flashing green dot in the right column next to "Battery status".