You can get a brownout even if you have a perfect battery. It is the voltage on the receiver bus that counts and that can be quite a bit less than the battery voltage. If the wire gage between the battery and receiver is to small or if the length is excessive or if the switch contacts are high resistance there will be a voltage drop between the battery and the receiver. Now it the servos put a sudden demand (you just commanded all of them to move at the same time and the air loads are high) the additional current demands drop the voltage on the receiver bus. This only need to last for a few microseconds to cause a brownout. You can not measure this using a typical meter, you must have an oscilloscope or some equivalent instrumentation to measure these short duration voltage drops. A Voltwatch comes close to meeting this demand. If you have the Voltwatch connected right on the receiver bus (no Y's or extensions) it responds quite fast. If you see the LED's dipping into the red when you cycle the sticks, it tells you that you have a wire, switch or battery problem or a combination of them. A Voltwatch is almost as good an indicator as an oscilloscope.