Should I dare watch this?
There are some interesting things, like a Spice battery model (they don't link any references, but
I googled it).
Then there are the bullshit parts, starting at 8:13: He draws a 100 mA current line and says the energy left is not the area under the voltage curve, but the area under the current line. Has nothing to do with how much power is left and of course, most modern devices needs constant power.
And as already debunked, at 26:38 they repeat that the Garmin device stops functioning after 1:52 hour, but the message on the screen is only a warning for the backlight. As firewalker
found out here, the message could be "The battery power is too low for full backlight. Use rechargeable NiMH or lithium batteries to prevent this limitation.". I did a screenshot and tried some filters to enhance it, and I'm sure this is the message:
Technically maybe you could say that lower backlight means "stop functioning", if they mean 100% functioning and the batteriser would indeed help for this device for this use case. Of course, without the batterise it might be possible to use the GPS device much longer, because the full backlight needs much more power, so this is reasonable for the firmware. But it looks like it does a peak detection. They should improve the firmware and do some average over some seconds, because from the current consumption diagram you can see that it works in constant power mode, so there is an internal boost converter. Short drops below the cutoff voltage doesn't matter.
For the scope part they are using a 0.1 ohm shunt (30:20 in the video: "for every one millivolt you get ten milliamps"). This would result in a voltage drop of 0.046 for the 460 mA, so at least they got this right and it doesn't matter that much for the cutoff voltage. The rest of the video is arguing, that the batteriser prevents such spikes. Adding a 10 cent capacitor, or fixing the firmware of the Garmin device, would solve this, too.
If a laywer would watch the video, they might not say anything wrong, but it is all very misleading and the batteriser is not useful for 99% of all devices.
PS: I'm one of the 10% who knew the right answer for the snail question