Li ion batteries require charging with a charger made for the purpose. They are susceptible to fire if not done correctly.
The charger needs to be able to monitor the cell voltage separately. Battery packs of multiple cells (laptop batteries for eg) have control circuitry inside to monitor each cell.
For home use it may be easier to charge separately and use in series.
The battery holder has circuits to protect from over and under voltage on the cells but probably not current control. Your supply would need to be current limited and voltage limited. The holder is only a backup protection not a charger.