I have a new ElectriFly 3 cell 640 mAh lipo that I am having trouble with. I charged it on my Hobbico Field Charger, and when I plugged it into my plane, it barely moved the control surfaces. I tried charging it again, but with the same results, and found that the battery voltage was only 7 volts. Any idea what is going on or what I can do?

A 3S with 7 volts is dangerously low. That may be why the charger did not charge it, although I think it should've thought it was a 2S and charged to 8.4 ? right?

Anyways I think it should have each cell tested and probably find out it is a junker or at least 1 cell is. It is risky to do anything with it.

Thanks. I plan to take it to my LHS tomorrow and have them take a look at it.

Also, it says on the battery "15C Max. Discharge" and "Never charge at currents greater than 1C". What does the "C" represent?

C just stands for "capacity" so that means 15 x 640 = 9.6 amps max discharge and .64 amps for max charge.

Go directly to Great Planes with your issue. You'll get quicker results than if you go through your LHS, and you'll be doing your LHS a favor, helping them to remain profitable. Great Planes will almost certainly send you a new pack and a postage-paid envelope to return the old pack.