Comments by "EebstertheGreat" (@EebstertheGreat) on "Asianometry" channel.

@wouldntyouliketoknow9891 The potential difference for a battery isn't constant at all. It varies substantially with its charge. If you take a typical 1.5 V cell as an example, it typically varies from about 1.65 to 1.20 V over its useful life, though depending on the application, you might be able to drain some more charge from it before it is effectively dead. For rechargeable batteries, you get the same problem: high voltage at high charge and low voltage at low charge, which electronics have to deal with. The actual energy that can be extracted from a battery can be difficult to calculate in practice and depends on the device you put it in. However, the stored charge is easily calculated, which is why that's what they report. Of course, in principle, the stored energy in a battery can be calculated with a relatively straightforward single integral, but the calculated value won't necessarily match the energy you actually pull out of it or the energy required to charge it, so it's just a nominal figure without much practical use.
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@craigslist6988 mAh is used in both marketing and in product design. This is because the current drawn by a device is usually specified in milliamperes. It's the same reason kilowatt-hours are used in power generation. Most people don't have an intuitive sense of how large a coulomb or megajoule is, and when calculating things for their own use, it makes far more sense to measure time in hours than in seconds. The reason units of charge are specified instead of units of energy is that they are easily verified and are application-independent.
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1:00 Not all materials have a bandgap. For instance, metals and other conductors usually have no bandgap. Graphene is an example of a semiconductor with no bandgap. However, all semiconductors commonly used in the electronics industry today do have a bandgap, though the gap is small for some semiconductors. I'm not an expert, so maybe there is some technicality when you get into impure materials that endows metals with some microscopic bandgap. But I think in principle, there is literally no bandgap at all, not even a tiny one.
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