This charger assures that the cells are 'balanced' at all times by charging them in parallel. When the cells are connected in parallel, any difference in charge level is equalized and they appear as a single cell to the charger. At all times during the charge, the cells are at equal charge levels.
This circuit will work with the USB / DC LiPo Charger
or the USB LiPo Charger V1.2
To accomplish this, we must disconnect the cells from the load. We use a 3-pole double-throw switch to simultaneously disconnect the load, connect the charger and switch the cells from a series to a parallel configuration. Charger output can be taken from any of the battery terminals via soldered connection or a JST connector.
In charging mode, the cells are connected in parallel to the BATTERY IN terminals of the charger. The positive side of the Load output is disconnected during the charge.
In run mode, the positive connection to the BATTERY IN terminal is disconnected and the batteries are re-connected into a series configuration. The positive output is re-connected to supply 7.4v to the load.