There won't be any need to disable the radio for unused bands. Powering down unused hardware is literally the first thing the engineers do to save battery life.
Edit: can't reply due to rate-limiting, but in principle, all they have to do to search for service is power up the receiver briefly, running at a very low duty cycle. This has no noticeable impact on battery life or any other aspect of the phone's operation.
Edit: can't reply due to rate-limiting, but in principle, all they have to do to search for service is power up the receiver briefly, running at a very low duty cycle. This has no noticeable impact on battery life or any other aspect of the phone's operation.