A Lithium battery cell is charged to 4.20V then it slowly discharges to 3.2V when it should have its load disconnected. Then its average voltage is 3.7V.
Maybe you have a Ni-Cad or Ni-MH cell that averages only 1.2V, but is charged to 1.4V or 1.5V?
Simply use a battery charger IC made for the type of battery cell you want to charge. You cannot simply measure the voltage because the voltage rises fairly quickly during charging but the cell is no where near fully charged because it is still charging with current.
A simple Lithium charger circuit can cause your home or car to burn down because when charged wrong a Lithium cell catches on fire. Lithium is a very active metal like magnesium (used in flares). The fire is very hot and is difficult to stop. Water on it makes it burn hotter.