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The vast majority of cell phones use a single-cell Li-Ion battery, so their capacities can be directly compared using mAh. Laptops almost always contain multi-cell Li-Ion batteries, so their capacity cannot be directly compared using mAh (e.g. a 4S battery rated for 2500mAh has more energy than a 3S battery rated for 3000mAh).
So why don't we use Wh for phones too? Simply because manufacturers would rather advertise a battery size of five thousand mAh (wow, so much capacity!) instead of 19 Wh.
The same issue happens with portable USB battery packs - they're all advertised in mAh even though they use a wide variety of chemistries and cell configurations internally. What manufacturers do is take the total Wh of the pack and convert it back to the equivalent mAh of a single-cell Li-Ion. It's annoying, and I really wish they would just use Wh directly.
But why not advertise in mWh? 19000 is bigger than 5000
I don't think they know about metric prefixes, Pip.
Imagine if the marketing people discovered that they could advertise that it has 19 million uWh (in Doctor Evil voice). Don't say it too loudly though, someone at Apple might hear.
Right, but mAh is 1/1000 of Ah, following the exact same thing
That would be ideal, but I think at this point there's just too much marketing momentum using mAh, and switching to mWh would be too confusing to consumers. But yeah, I agree, mWh is definitely the most appropriate unit to use.
five thousand mAh
Isn't that just 5 Ah though
Yeah, but it's 5 billion nAh.
I spent billions of nanodollars on lunch today
Well I spent trillions of pico dollars.
And 19000 mWh. I'd rather have 19000 of something rather than 5000. I feel cheated and no amount of telling me it's exactly the same will change my mind.
Yeah but then you don't get to say thousand
Goodbye dream of knowing how many times my car can charge my phone.
19000 mWh!?!? I have to get that phone!