I has a 14 hour timer that starts when you plug the adapter into the radio and turn the radio off. If you turn the radio on again, then back off, the timer starts over. The charging is on, or off depending on the battery setting in the compartment and the adapter is 6V, 800mA.
I use an external charger for all of my radios that use AA's. No good reason to use your ~$200 or ~$500 radio as a batery charger, except when you don't have a charger around.