5 ms·

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

by darken 3y ago

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

zelon88 3y ago
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 3y ago
  No one? Just like no one explains that the 1.2v 1500mah battery isn’t compatible with the 9v 1500mah battery.
  - deleted 3y ago
    [deleted]
- deleted 3y ago
  [deleted]
dgacmu 3y ago
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 3y ago
  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).
  - tivert 3y ago
    > 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 3y ago
      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 3y ago
        > 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-Charged-Rechargeable/dp/B00JHKSMJK https://www.amazon.com/Panasonic-BK-4MCCA4BA-eneloop-Pre-Cha... https://www.amazon.com/PANASONIC-BATTERIES-CR1216-LITHIUM-BATTERY/dp/B00HKJPZKO https://www.amazon.com/PANASONIC-BATTERIES-CR1216-LITHIUM-BA... https://www.amazon.com/SR521W-SR521SW-LR521-Alkaline-Battery/dp/B076ZHHKTZ 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.
amluto 3y ago
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.
throw0101b 3y ago
> 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 3y ago
  Most lightbulbs in Au display brightness in lumens and power in watts. I think it makes sense to show both.
trashtester 3y ago
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.
karmakaze 3y ago
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)

by darken 3y ago

zelon88 3y ago

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 3y ago
No one? Just like no one explains that the 1.2v 1500mah battery isn’t compatible with the 9v 1500mah battery.
- deleted 3y ago
  [deleted]
deleted 3y ago
[deleted]

dgacmu 3y ago

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 3y ago
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).
- tivert 3y ago
  > 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 3y ago
    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 3y ago
      > 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-Charged-Rechargeable/dp/B00JHKSMJK https://www.amazon.com/Panasonic-BK-4MCCA4BA-eneloop-Pre-Cha... https://www.amazon.com/PANASONIC-BATTERIES-CR1216-LITHIUM-BATTERY/dp/B00HKJPZKO https://www.amazon.com/PANASONIC-BATTERIES-CR1216-LITHIUM-BA... https://www.amazon.com/SR521W-SR521SW-LR521-Alkaline-Battery/dp/B076ZHHKTZ 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.

amluto 3y ago

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.

throw0101b 3y ago

> 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 3y ago
Most lightbulbs in Au display brightness in lumens and power in watts. I think it makes sense to show both.

trashtester 3y ago

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.

karmakaze 3y ago

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)