I have key pad entry on the deadbolt only. Door knob does not lock. I used to fix doors after break in s and realize that both locking is not needed. If they break in the deadbolt the locking knob is not going to stop them!
The batteries last over a year and if you change them say every 6 months should not be a problem. As other poster said you should have a key as back-up. I actually do not have a key for the key pad, but for the other door if needed.