I believe it actually has to do more with historical conventions in electronics or math. (This is just what I remember from heresay when I was in university as an electronics engineer), but there is also a mathematical reason.
history hearsay theory
The easiest way to measure power draw is by measuring current draw (voltage across a sense resistor) way back before there were affordable, quality ICs to measure voltage and current and pretty much joule count.
To add to this, current sensors are much easier and cheaper than test machines that do the calculations for you.
When lithium batteries and NiCAD batteries became standard compared to the earlier lead-acid (which are measured in Wh), they had an extremely flat voltage curve compared to lead acid. They could be considered to be at a constant voltage.
Now cheaper electronics were being made and if a designer wanted to know how long a battery would last, they could take the nominal battery voltage that the battery would be at a vast majority of the time, and they could just measure the current draw over a short time of the circuit, 10s of calculations, and you have your approximate battery life. There is a joke that engineers approximate π to 3.
Even designing electronics today, everything is specced to current draw, not power draw. ICs take X current in mA during Y operations. Your DCDC converters have Z quiescent currents and from there you can calculate efficiency. It is much easier to work in current for energy running through the circuit.
Math units
Ah is a measure of electrical charge.
Wh is a measure of energy
Batteries and capacitors hold charge so are measured in Ah, generators that power the grid generate energy and use of that energy is measured in Wh (it also isn’t a “constant” voltage source like batteries as it is AC)
The thing is, it does not matter how much charge the battery holds, it does matter how much energy it holds. Without knowing the Voltage the Ah is useless.
Sorry, but you are simply wrong. Simple math says that you are wrong.
You can buck or boost convert nearly any voltage to any other voltage.
Then measure the current output of the battery, boom you have battery life.
Also electrical charge can be used in many, many very valuable calculations without involving voltage at all.
Let’s take an arbitrary example with an arbitrary battery powered device. Let’s say the battery is somewhere between 1V and 10000000V. You can’t measure it because you might blow up your multimeter.
You know that the battery is 5000mAh. You can safely measure that all of the circuitry is draining 1000mA because sense resistors or contactless magnetic current measurements don’t have anywhere near dangerous voltages. You know that the battery will last about 5 hours. What is the voltage? Doesn’t matter.
Yes, charge and the flow of charge is not the entire story, but to say it is useless or does not matter is just a straight lie. It is fine if you don’t understand electronics, but then don’t spit out misinformation.
Yes Watt-hours would give a more complete picture to slightly tech-inclined consumers (makes 0 difference for 99% of consumers), but then it returns to not mattering because you can do the 5s calculation yourself because single cell lithium batteries are overwhelmingly 1 nominal voltage.
Literally 90% of calculations related to efficiency are JUST as valid using mA as W.
Your device uses 12mA at idle with a 5000mAh battery has the same relevance as your 18.5Wh battery using 45mW at idle.
I am ONLY speaking from a consumer position and for those Wh is more useful.
The consumer looks on device a and on device b and then determines how often he can recharge its device. With Ah you cannot do this unless you know the Voltage, with Wh you can make this decision without any further knowledge.
Yes this does not include battery life or conversion of efficiency. But a cunsumer measures nothing he looks at the lable.
It is fine if you don’t understand electronics, but then don’t spit out misinformation.
Btw. no need to insult me. I have never put out misinformation, I may have not stated enough that I am viewing this as a consumer.
