[darken]

This has bugged me for so long and I hope the industry finally stops someday.

To summarize for anyone not versed in electrical power:

* mAh measures how much current your battery holds, irrespective of voltage.

* However, actual POWER is measured in Watts (or watt-hours cumulatively).

* Watts = current * voltage.

* A 2000mAh hour battery at 2 volts has half the power of a 2000mAh battery at 4 volts.

* As voltages can vary based on battery arrangement (parallel vs series cells), this makes a huge difference. You can half or double your mAh by arranging your cells differently, without changing actual power stored.

Using Wh or mWh instead of mAh would make this whole problem go away. But then that means low voltage batteries (like often used in phones) can't inflate their reported mAh compared to high voltage cells (e.g. in power tools). They also tend to conveniently leave out the battery voltage, so you can't tell when it's an apples to apples capacity comparison.

It's so silly. /rant

[dgacmu]

I 99.9% agree with you. Some nitpicks, since this is a discussion of getting units right:

mAh doesn't measure "current", because current is the flow of electrons. It measures charge.

2000 mAh hour is redundant - the 'h' in mAh is hours. :)

But your basic point is 100% correct: All batteries should show their capacity in Wh.

[coder543]

It's also redundant because with 2000mAh... "thousand milli" can just be eliminated, leaving us with 2Ah.

Everyone constantly referencing thousands of thousandths is another one of my "favorite" things about the industry using mAh as a standard measurement of battery "capacity" (besides the fact that they almost never specify voltage or watt-hours).

[maxnoe]

Don't quote capacity. It is the correct tern, physically. Capacity is the amount of electrical charge something can store, Ah is unit of that. Not the natural unit though, that would be Coulomb (C).

Why use Charge and not energy? Because the voltage changes as the battery is discharging, so it's not as straight forward as just multiplying with the voltage.

[coder543]

> It is the correct tern, physically.

Agreed, but not from a consumer perspective, where it is very confusing that a battery with half the capacity might have twice the energy due to differences in voltage.

From a consumer perspective, the battery capacity is the amount of energy, regardless of whether that is wrong.

[TT-392]

I don't think "capacity" neccesarily has a concrete unit connected to it. I am pretty sure you could call both the charge and the energy in a battery its capacity.

[paholg]

> Not the natural unit though, that would be Coulomb (C).

To be pedantic, you mean SI unit. The natural unit of charge is the electron (e).

[tivert]

> It's also redundant because with 2000mAh... "thousand milli" can just be eliminated, leaving us with 2Ah.

But then you'd have to do more conversions when comparing. I've seen batteries with capacities as low as 10mAh. 4 digits is still a reasonably practical number.

[coder543]

In the consumer space, virtually no battery I've seen in more than a decade is less than 1000mAh. If you looked at the Reddit post, you know we're talking about laptops, tablets, phones, external power banks, that type of consumer-facing application. But, even then, converting is fine. People understand there are 1000 meters in a kilometer. I don't think any of this is rocket science.

However, outside of the consumer space... doing conversions like that is also fine. When browsing DigiKey, components are often listed in the optimal unit prefix. When necessary (not so much with batteries), the interface allows you to filter based on ranges you provide, and it will perform the necessary conversions for all the products to give you an accurate list.

[tivert]

> In the consumer space, virtually no battery I've seen in more than a decade is less than 1000mAh.

Behold:

https://www.amazon.com/Panasonic-BK-4MCCA4BA-eneloop-Pre-Cha...

https://www.amazon.com/PANASONIC-BATTERIES-CR1216-LITHIUM-BA...

https://www.amazon.com/SR521W-SR521SW-LR521-Alkaline-Battery...

> People understand there are 1000 meters in a kilometer. I don't think any of this is rocket science.

Yes, but it's one more mental operation, and every mental operation like that is relatively costly. People don't actually have that many slots of working memory. You are optimizing to minimize digits, which is probably the wrong thing.

[coder543]

>> virtually no battery

> Behold <a single counterexample that is far less commonly encountered by consumers than phones, tablets, laptops, or external power banks>

EDIT: Ok, now you have updated your comment to also include coin cells, which is even less relevant. This just shows you don't appreciate what we're talking about here.

Consumers care about the amp-hour capacity of larger devices for various reasons. They need to figure out how many times they can recharge a phone from an external power bank. They want to understand how much less efficient their laptop is than their tablet. That's not what they do with coin cells or AAA batteries.

You have also ignored that we can express 0.8Ah. It doesn't have to be 800mAh vs 2Ah. Since things less than 1Ah are far less common for consumers, it would be logical to just show everything in Ah, and then represent those smaller things as fractional Ah, if we're afraid of multiplying and dividing by 1000.

We could represent all distances in millimeters just in case, but we don't.

[hulitu]

> "thousand milli" can just be eliminated, leaving us with 2Ah.

They call it marketing.

[Joker_vD]

Have you ever heard the word "half-pair"?

[amluto]

For future rants: mAh is a measure of charge, not current. And batteries don’t have “power stored” — they have “energy stored”.

When you make a statement like “A 2000mAh hour battery at 2 volts has half the power of a 2000mAh battery at 4 volts,” it’s a bit nonsensical — a battery does have a certain amount of power available, but that amount is not charge * voltage, nor is it even necessarily proportional to the energy stored.

[karmakaze]

Historically batteries have had known standard voltages (12V, 6V) and within that context, mAh is easily convertable to Wh.

With USB PD and powerbanks etc that operate at many voltages using mAh is unclear. It's only used historically as a number comparable to previously used numbers. As someone mentioned the implied voltage is that of the cell 3.7V

So the conversion formula is Wh = mAh/1000 * 3.7V (or substitute the standard voltage for the context)

[trashtester]

The main problem with your argument, is that for many use cases, the real voltage from a battery is not identical to the nominal voltage. As the current through the battery increases, energy loss due to the internal resistance of the battery will cause the external voltage to go down.

This means that actual Wh will depend on how many amperes the battery has to deliver. When the load is very low, this hardly matters, but when you need to power a high wattage engine/appliance with a small battery, this can be quite significant.

[throw0101b]

> Using Wh or mWh instead of mAh would make this whole problem go away.

Amp-hours (Ah) has been the 'standard' way to list battery capacity for decades, see for example the boating/marine world. I'm not against changing it to something else, but there's a long-tail of legacy here.

Also, while we're at it, can we change away from listing the brightness of light bulbs in watts: this may made sense with incandescent bulbs initially, but we're not beyond those.

[perilunar]

Most lightbulbs in Au display brightness in lumens and power in watts. I think it makes sense to show both.

[zelon88]

So who's going to explain to 99.999% of the world why a 10w/h battery that is 5v is incompatible with their 12v device that also takes a 10w/h battery?

[dv_dt]

No one? Just like no one explains that the 1.2v 1500mah battery isn’t compatible with the 9v 1500mah battery.