Yeah, I know of Exponential. (Fun fact: their quasi-successor company, Intrinsity, ended up getting bought by Apple, and is one of the companies among PA Semi that presumably ended up forming today's Apple Ax design division.)
I knew I was going out on a limb on that one. Sorry for the mixup!
I honestly have no idea how Jury came up with the oddly specific number of 7000 mAh, or why they think that won't be particularly heavy.
I do think a good case can be made that the Magic Keyboard for iPad Pro should include a battery. But the original implication was that Apple only didn't include one as a cost-saving measure; that's clearly not so. Either the added weight would be significant, or the added battery capacity would be useless.
Well, the pass-through is already there. (A bit of a confusing design choice, honestly. You get a USB-C port, but it can only be used for charging.)
I searched the other day and found
this power bank. It's exactly 7000 mAh and weighs 159 grams. Let's say Apple is a bit more efficient than that; they can save some of the case, after all. Your 150 grams would still be right on the money. It's not gonna be below 100.