It sounds like your battery is a Lithium Polymer and not Lithium Ion. Lithium Polymer batteries have a nominal voltage of 3.7v per cell which is why yours says 2s 7.4v on the label.
I use LIPOS a lot and only ever charge them on a LIPO charger making sure that the balance connector is plugged in. LIPOS are extremely dangerous if not charged properly so beware.
Good luck
CaptB