3.8V per cell is about the proper storage voltage. Are you sure that the charger is setup properly?
It's a 45 watt rated charger.
For the 2 cell Lipo, 8.4v should be the full charge voltage. The charge current may cut back
to prevent the charger from going above this voltage.
While a 5200mah pack can easily accept a charge current of 5A, it can only do so when the charge voltage
at 5A is no more than 8.4v or so for a two cell pack.