I get that, for a house/solar battery, it sort of makes sense as your typical energy usage would be measured in kWh on your bills. For the smaller devices, though, the chargers are usually rated in watts (especially if it’s USB-C), so why are the batteries specified in amp hours by the manufacturers?
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Amp-hours is a measure of charge, Watt-hours is measure of energy.
It’s really easy to measure how much power a device is draining in a house (a 100W bulb is drawing 100W of power, so in 1 hour it uses 100Wh of energy) we don’t care about what voltage or current its drawing, just the power. The electric company also isn’t charging use based on how much charge we use, but rather how much energy we use.
A battery can only hold so much charge, and once it’s spent, it’s gone. We could have gotten any amount of energy out if that because energy losses can vary a lot, and the current you draw from the battery can vary a lot, so it’s easier to express how much the battery holds in Ah rather than Wh.
If you want to convert between the two, V * Ah = Wh but this won’t account for energy losses.
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