I think at least this time, CircuitGuy has it.
Some years ago (25?) my local auto parts store sold a battery life extender, it was a bottle of some unspecified liquid that you poured in each cell of your car battery.
My 3-year old battery failed completely within one week of that treatment.
'Once bitten, twice shy'

Is this a joke? If the product uses a voltage-based fuel gauge chip, and you boost the voltage, of course you fool the chip.
"Roohparvar used an Apple Magic Trackpad to demonstrate Batterisers. He metered a pair of AA cells and they read 1.3V; Apple’s app reported that the batteries needed to be replaced. Roohparvar slipped on a set of Batterisers and metered again: 1.5V, enough to convince the Mac that the Trackpad was running a new set of batteries with 100% charge."

I like the part about how the battery companies are trying to buy him out.

If this product were real, people we be breaking down his doors to get them. "They kicked in the front door and stole samples" LOL

This only is beneficial if the device you're powering has way too low minimum input voltage.

They're saying most devices have a minimum cell voltage of 1.3V, but this has not been my experience. Most products run with cells at 1.2V, otherwise you would not be able to use NiCads or NiMHs, which have a 1.25V nominal voltage.

This boost converter device might be useful for running devices with very high minimum input voltage. It would have to be pretty bad, though, because you'll lose something in the boost converter, the boost bypass, and the comparator that checks whether you need boost. That must run all the time and pull at least a few microamps. .

That's astonishingly vague. "like those little clips that go over the end of the toothpaste tube so you can roll them and squeeze out ever last glob of paste."