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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I see a lot of people saying mAh is a scam. It most definitely is not.
To simplify matters i will Ah (Amp hour) and Wh (Watt hour).
I will start it simple, the very basic law of electricity, Ohm’s law: V= I * R. Meaning Voltage (measured in Volts) = Current (Amps) * Resistance (Ohms)
Since we have quite constant voltage noawadays, this form is more relevant I=V/R
And last in the introduction is the Watt: P=V * I … W = V * A
Since pretty much every phone sports a “3.7V” battery, it’s very relevant to compare them at mAh because batteries have traditionally been for Ah. A 3Ah battery basically means that a full battery will last for 1 hour if you draw a 3A load or 3 hours if you draw 1A. In this whole paragraph, voltage doesn’t matter. You could try this setup with a measure of current, never checking for voltage as long as you keep the load constant.
Cars and houses on the other hand use complex battery packs which are basically made from smaller batteries and the batteries can be arranged in SERIES or in PARALEL. If you arrange 2×3.7V batteries in series, the Voltage will double while the Ah will remain the same. You can basically drive bigger loads for the same amount of time. But if you arrange 2×3.7V batteries in paralel you get the same voltage output but you double the Ah so you can drive the same load for twice as long.
The bettery packs are arranged in such way to have a voltage output relative to the load, so a hybrid car might have an 80V battery pack while a full electric car will run it’s battery pack at 800V. House batteries generally use the same technology the car batteries but the problem is your house normally runs at 110/230V so you have smart and fast electronics that step it down or boost it up depending on your needs.
TL;DR voltage doesn’t count in Ah ratings but it does in Wh ratings
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