16 hours charge time
My DX7 usually is at about 10.9-11.2 right when I take it off the charger..(like this morning..).. and at the end of the day.. about 7-8 flights total(2 different planes).. its at 10.4.
I agree with DGrant. The transmitter will work down to something like 9 volts, but that doesn't mean it's safe to fly at those levels. Once you get below 9.6, the drop off can be quite rapid, especially if you have a weak battery.