A 2 cell A123 is rated at 6.6 volts and will work fine as a receiver battery without a regulator.

Everybody has their favorite battery set-up and I don't wish to start a battery war here, but I use 5 cell nicads in all my planes and am in no hurry to try A123's. They cost about twice as much and weigh about half as much as nicads. A friend crashed because he was using a battery chemistry he wasn't familiar with. If this is your first jet and you don't already have an A123 capable charger I would recommend sticking with nicads, you'll have enough of a learning curve with everything else. You shouldn't need a lot of battery capacity batteries on a plane like the Jetmach 60.

Joe