I would be cautious about using a simple volt meter to test the capacity of either a flight pack or a TX pack.

You need to load test them. No probs on the TX - switch it on and Anything less than Green or 9.5 volts DO NOT FLY.

TO TEST THE FLIGHT PACK UNDER LOAD IS TRICKY IF YOU JUST WIGGLE THE STICKS TO MOVE THE SERVOS.

The readings will be all over the shop. Much better to buy a little battery tester for about 20$ these apply a load and give you Green Amber Red

Do not fly if in the red OR the bottom amber.