RE: DX7 TX Charge/Discharge
The Tx guage just tells you the Voltage of the battery. While that is important, it does not accurately predict how well the battery is holding it's charge.
If I get a hint that my Tx battery may be discharging too quickly, I will Cycle the battery to be sure it is Charging and Discharging properly. I am not saying to do this every week or every month. A lot depends upon how often you fly, how often you charge, and what type of Tx batteries you use.