The wall-wart will NOT do an adequate job of charging 6 volt packs.

The DX7 displays the system battery voltage in the upper right corner of the LCD. Remember that this is ONLY the TX voltage and has ABSOLUTELY no bearing on the condition of the RX batteies. The TX can be fully charged and the RX dead.

You can use aftermarket chargers to take care of the batteries but don't fast charge unless you need to. The batteries will appreciate it.