Where are you monitoring the Voltage, the CB200 or the Receiver ? There is a battery share circuit that drops the voltage to the receivers by about .6 volts so that could be contributing to your problem. Still, I find even monitoring the individual battery voltages in the CB200 I need to set my low voltage alarm to about 6.6Voltage to avoid low voltage alarms during extreme maneuvers that require all control surfaces to be deflected at the same time but that is in 40% aerobatics airplanes which are spiking to over 15A per receiver battery at the time. Take a look in the log file to see what is going on and it should be pretty easy to figure out.