Charging using 120V power supply in Europe?

Based on what I read in and between the lines, I would not do there! Chargers are usually made with current limiters in order to protect the battery. Your charger is made to work with your helicopter, and if you are not exactly sure what you are doing,you risk damaging your toy. A voltage converter on the AC side is much simpler and safer. They should not cost too much, as they basically consist of a transformator.