Well thats a lot of battery, but like I said your wall charger wont charge it to 6 volts,,,as far as I know, unless you have a separate charger,,my wall charger shows 9.6 volts for the radio and 4.8 volts for the receiver battery...Rog
make sure you dont plug the battery into the rx backwards as that will fry it!!
On the side of your rx it should show -/+/u which is (on the servo) black/red(sometimes black with red stripe)/white