That's if a leak from a Chinese certification database (first reported by MySmartPrice) is to be believed, indicating that the first generation of Apple's outdoor-focused smartwatch will feature a 542mAh unit.
Apple doesn't ever officially release battery specs concerning its smartwatches, but the database reveal suggests that this represents a big jump from the Series 8, which sits at 308mAh for the 45mm version. For the 41mm version, that dips to 282mAh.
Of course, what Apple does always reveal is the hours you can expect from its smartwatch, which is why these battery specs aren't necessarily a huge surprise.
Given that the Apple Watch Ultra is quoted at 36 hours - double the usual 'all-day', 18-hour life of the company's standard smartwatches - the jump does appear to match up.
Interestingly, to gain what should end up being roughly 100% more battery life from less than double the overall battery size also suggests the Ultra's battery is also more efficient.
As we've hinted, though, while specs are one thing, how this all shakes out in real-world use is another.
We're currently putting the Apple Watch Ultra through our testing process, and we'll have our full verdict - including a comprehensive battery comparison - over the coming weeks.
How we test