I think it's an "upgrade" and not included in the base. But it's true, and neat!
If your vehicle is on the charger and power goes down... It'll auto switch you over to the Ford's battery. They say it lasts 3 days... But I don't know if that's 3 days of normal usage or limited - either way... It'd be nice, if you run out of juice in 2 days... Hop down to a super charger for a few hours and make it back before all your food spoils. We don't have outages too often, not enough to buy a real generator - but it's enough to lean me more in Ford's direction than Tesla's.
[Edit] looks like all lightning's can do it, you.just need the 80 amp charger that comes standard with the luxury ones... Or you can buy it yourself, for $1300... Not a bad price, but would be nice if they include it when you're buying a 70k truck.