Possibly. But you would never charge such a battery anywhere near full, and it wouldn’t be used at all unless something did happen. It would be largely useless of course, except in rare instances, but it could be checkbox benefit over the competition, and give piece of mind to all oldtimers who have experienced corrupted rust drives even if it were because we cut the power ourselves in a less than considerate fashion.Since it will almost always be connected to power, the battery would tend to dgrade pretty quickly. And they swell up, etc. Just one more thing to break, adds to cost, etc. And often not needed, either because you have a bulletproof grid, or you have backup generators, solar, or a UPS. Not worth the hassle.
Not that I have ever done so myself of course (*cough*).