seems that you trying to charge litium with constant voltage. if your voltage won't go higher than max charging battery voltage it will work. but as u said it is taking ages. it will be that way. for max voltage alowed for lithium it depends on chemistry, so to find out look for battery characteristics from manufacturer, or google it.
For normal litium cherge u need to keep constant current (usualy up to 1C) untill max battery voltage is reached on bettery terminals. then swich to constant voltage till current will drop till 0.01C or something like that.
also there r other more exotic ways to increase charging current but maybe not this time.