If the fixture is switched then an additional un-switched conductor is required to charge the battery and tell it when normal power is available so that it doesn't switch to battery power when the light switch is off.
Factory installed em ballasts will be a long lead time. We field install a lot of them. We figure an extra hour per em ballast for field installing them. You can often get loose em ballasts cheaper then factory installed also and make some money installing them in the field.