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.

Generally Li-ion (3.7V nominal) batteries were used so they could just base it off of current usage rather than power usage and you could get a decent idea comparing between smart phones.

Laptop batteries tend to use an operating voltage of multiple times that (2-cells would use 7.4V-ish, 3-cell would be 10.8 to 11.4V nominal, 4-cell would be 14.8V and so on), but the number of cells can vary wildly per model, so Wh is easier to compare numbers between laptops.

mAh is a bigger number than Wh and looks better on packages.

Can I add a follow up question: Why don't normal batteries have any useful measurements on them, at least in the UK anyway, not sure about elsewhere. Rechargeable batteries will have an Ah rating but normal AA or AAA etc will just say "Ultimate" or "Advance" etc, like why can't we just have an Ah or Wh or even just a standardised rating based on a fixed current discharge or something? It's infuriating that in 2023 I'm buying something with know way of quantifying its content other than the inference of the product name.

This shit should be all standardised around [micro|milli|Ø|kilo|tera]joules. mAh isn't even energy, it's charge!

The same exact reason ISPs sell bandwidth in Mb/s, instead of the proper unit.

Quite simply, 500Mbit/s sounds a lot more impressive than 0.5Gbps or 62.5MB/s.

Laptops predate cell phones in mainstream use. When laptops started, there were a variety of battery types in use with no standard charging voltage so Wh was the fair way to compare.

Cell phones have pretty much always been 3.7v lithium so mAh is a fair comparison and gives a bigger number than Wh.

Wh is a unit of energy, Ah is a unit of electric charge, basically how many physical electrons passed by.

The voltage of a battery goes down gradually as it is discharged, so getting an accurate value for total energy dissipated is very complicated, as this varies greatly with the discharge profile and other physical factors like the age/health of the battery.

The one thing that stays constant is the amount of electric charge a battery can provide. If it's old, the voltage of that charge will be lower and go down quicker, but it will be the same total charge.

I agree from a consumer point of view, joules would be a friendlier unit, however it is also a lot easier to game. Electric charge is a much more definite unit in an electrical engineering sense.

If any of what I said is confusing please ask me to clarify, I'm assuming a basic level of electronic literacy but it's hard to know what knowledge I'm taking for granted as an ex electrical engineer.

For the same reason Audi didn't sell the Audi "5", Pontiac never sold a "6LE". and Saab didn't try to sell the "9 turbo". It sounds more impressive with the zeros added.

Why 5000 mAh rather than just 5 Ah?

My laptop shows the battery capacity as 8790 mAh.

Aren't most notebooks measured in gsm?