Why not just use Wh?


#1

There’s something I have a doubt on.

According to what I know, to know the wattage (or Watt-hours) you need both mAh and the voltage of the battery.

Wh is also the measure that shows you the real energy capacity of a battery.

So, why do smartphones generally present their batteries in mAh and laptops in Wh?


#2

I was also interested in knowing this as well, so I did my own research, here is what I have yielded:

TL;DR: Laptop Batteries are multi-cell so they have to use Wh, and Phone batteries are single cell so they use mAh. As to why, you’ll have to check out the link above.


#3

And another important part is that phone batteries normally have a voltage of 3,7V and hence you can compare the energy capacity different phones have just by comparing mAh. :slight_smile:

Thanks for the link!


#4

You’re welcome! Happy to help out! :slight_smile:


#5

Yeah I would say that’s one of the biggest reasons phone batteries use mAh. In reality, it would be more accurate to state all battery capacities in Wh, as the Watts figure includes both the amperage and the voltage rather than just amperage.


#6

If one wanted to be cynical, one might also say that the use of mAh is a way to make the numbers look bigger and therefore make the marketing easier, as mWh is a much rarer convention than Wh or mAh… :wink:

From a physics/engineering point of view, it’s not so simple to convert from mAh to Wh, though: the voltage of a battery changes as it discharges. I’m guessing that mAh are easier to compute using a standard procedure (hook up a batter to a constant-current source and just see how long it takes to discharge), whereas Wh requires factoring in the voltage curve. But from a user perspective, Wh is probably more important: it’s how much energy is actually in the battery… Although of course for a laptop that really depends a ton on the device and how it’s getting used.


#7

Yeah that was going to be my next point, that Ah is a lazy man’s measurement, while Wh is a more comprehensive indicator of how well the battery actually performs.