When fully-charged, an 8-cell NiCd battery pack can read as high as 12 V. Usually, though, you'll see it above 10 V for quite a while before it drops below that. If the pack gets to about 9.6V or so, you may wish to stop using it and recharge.

You can discharge a battery pack by removing it from the transmitter and putting it on a discharge analyzer, or just turn on the transmitter with the antenna up and allow it to run down.