Agree that VoltWatch is great. I use them consistently in all my NiMH equipped planes. BUT... I have now moved to LiFe, with 6.6v nominal. They have a very flat d/c curve so neither a VW nor an ESV are of particular value. One just has to keep track of the mAh used per flight, and stay under battery capacity with some safety margin.

Giant scale - sounds like you do not have dual switches. Many guys at my field with the larger aircraft use twin battery packs, and twin switches. On failed battery or one failed switch will not take down your plane.
That approach is a little problematic on small (.40-.60 sized) birds, but appears feasible for 1/4 scale and above.