How many rechargeable AA batteries do you need to make 9v?

I believe that AA batteries are rated at 1.5 volts each, so if you were to take 6 of them and wire them together in series that would produce a circuit that's pushing 9 volts.

But recharge AA batteries are only 1.2 volts per unit so a little lower voltage will be the result. I think most devices will still work on the lower voltage. Also these batteries will never last as long as the regular dry cell.