We don’t actually know yet what the purpose of the battery will be.
Vera, a Z wave only controller that has been around for a while, has battery power which is not used to back up the hub during a power outage, but rather just used for a few minutes at a time so that the hub can be taken very close to devices that are already installed, like door locks or wired light switches, to pair those. Door locks are particularly problematic, because they use a security protocol and will only pair to the actual hub, not a remote controller like the Aeon Minimote.
As you can imagine, that particular feature is especially helpful if someone either is migrating from a competing hub, like Vera, and already has their devices installed – – or, if they were upgrading from a version one hub, and there was no migration utility yet.
Although some people have assumed that having a battery meant having the ability to operate the hub for several hours, SmartThings has not announced that, and that’s not what some of the competitors offer.
So we’ll just have to wait and see what actually arrives.