RE: Unexplained loss of control
Giant scale and 2000nimh don't go together really well. The NIMH can't always provide the current required because of internal resistance. I would go with A123 or at least hi capacity LIFEPO4. There are many LIFEPO4 packs that are 6.6 volts nominal, 2000mah if you wish and 20-30C discharge capable which would do what you need.
Several radio people indicate NIMH is not the way to go.