RE: how to to tell voltage
Just to clairify here... You've listed 2 that are nimh/nicad cell voltage combos and a lipo cell voltage.
The 4.8v can be made from 4 AA or Sub C cells, either nimh or nicad (4 x 1.2v). AA cells are used for receiver packs.
The 7.2 is a standard 6 cell nimh/nicad sub c pack ( 6 x 1.2v)
The 11.1v is a standard lipo pack (3 x 3.7v). Very difficult to build your own packs as you have to put in a balance plug and lipo cells are a bit more dangerous to work with, especially shorting them. The closest in a sub c pack would be a 10 cell pack which would give 12v or 9 cell which gives 10.8v.