Battery life for the four AAs is rated for a year, and you've no need to worry about being surprised by an outage, either: the system will notify you well in advance using the lock's eight RGB LEDs or through the app.
We're not missing the old "gamertag recovery" feature the cloud system replaced and upgraded, but any significant outage is certainly enough to make us think about keeping our saves backed up on a memory card in a safe place -- just in case.