RE: 6 volt battery question
That depends on the capacity (mah) of the pack and what you are putting it it. A 6v battery wont last as long as a comparable 4.8 pack but its not a lot of difference.
A 1000mah 4.8v pack on 3d plane with high torque digital servos will not last as long as a 500mah 6v pack on a trainer with standard servos.