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The ones saying this is a mistake are scientists and electrical engineers. They know what a w/h represents as a unit of measure. They have the frame of referenc

The ones saying this is a mistake are scientists and electrical engineers. They know what a w/h represents as a unit of measure. They have the frame of reference and know the equation. So they would rather see a standardized measurement that takes into account all factors in one measurement. But you don't use batteries like that. Consumers use batteries that are a specific voltage. Watt hours obfuscates this fact. So when a user tries to plug a 1.2v 40w/h battery into a 12v device that takes a 40 w/h battery, they will not know why it does not work. So we break it out into two separate, and unequally important properties for these consumers. The important property being voltage. If the voltage is the same, the battery can be considered by consumers to be "compatible" with their device. If the mAH is greater, they will have more battery life. Lower, and they will have less battery life. W/H is insufficient for describing batteries unless you specify the voltage you are working with. People don't care about potential energy unless you tell them it's important. That's why batteries are represented as # of amps per hour @ a specific voltage. Also, thank you for reminding me of how terrible and sophmoric Reddit is.

spookie 3y ago
Yup, that makes perfect sense
nicoburns 3y ago
There is no such thing as a device that takes a 40wh battery. A device will take a battery with a specific voltage, and will last for different amounts of time based on the capacity.
fanf2 3y ago
Your theory might make sense if the voltage was actually specified, but when I last bought a USB-C power bank I could not find that information anywhere, so I did not know if I was comparing like with like.
- jfengel 3y ago
  In a saner world, it would be implicit in the USB-C. As it is, you know that it supports 5V. It might also support higher voltages (up to 20V), though if it doesn't specify I wouldn't assume. If you need higher voltage, you'll have to look for a battery that specifies it. (And hope that the package isn't lying.)
  - soneil 3y ago
    Every powerbank vendor I've seen gives the battery rating at 3.6/3.7V, so USB implying 5V gives us misleading values. So a 20,000mAh powerbank is 20*3.6V=72Wh, not 20*5=100Wh. I've never seen a vendor that specifies 3.6V, the best you can hope for is that they give mAh and Wh so you can derive it yourself. If we need the Wh rating to keep the mAh rating honest, the mAh becomes redundant before the Wh does.
- chrisnight 3y ago
  I’m not sure where you live, but I believe every battery sold in the US legally is required to label their I/O voltage and amps, and capacity voltage, amp hours, watt hours. At the very least, every wall outlet and power bank I’ve seen has text somewhere that tells what it outputs, with the powerbanks aswell having capacity, both amp hour and voltage. Though I will say the text is rather small.
  - fanf2 3y ago
    The description of a typical power bank leaves voltage and watts implicit, as far as I can see https://www.amazon.com/dp/B07S829LBX/ https://www.amazon.com/dp/B07S829LBX/ I mean, I can work out what they probably are with a little general knowledge and arithmetic, but it isn’t as clear as you suggest.
throwaway894345 3y ago
> So we break it out into two separate, and unequally important properties for these consumers. The important property being voltage. If the voltage is the same, the battery can be considered by consumers to be "compatible" with their device. If the mAH is greater, they will have more battery life. Lower, and they will have less battery life. It works exactly the same way if you replace mAh with wh.
ilyt 3y ago
Devices don't say "It needs 40Wh battery" Devices say "it needs AA battery" or "It needs 18V battery" >W/H is insufficient for describing batteries unless you specify the voltage you are working with. Yes. Then do exactly that. Describe Wh and voltage.
- pas 3y ago
  Just describe Joules. No need to bring hours into it.
  - vel0city 3y ago
    Not everyone likes to think about how many seconds their devices will last. Hours are a lot easier to reason about.
- firebat45 3y ago
  There are two important numbers when it comes to batteries. Volts and Amp/hours. Watt/hours is simply a calculated value. Why provide watt/hours and force people to back-convert to amp/hours? Watt-hours is only useful when comparing batteries of different voltages, which is not a very practical thing to be doing. For batteries of the same voltage, amp/hours is a simpler and easier way to compare.
  - stetrain 3y ago
    What voltage is your laptop battery? Your smartphone battery? Your Anker power bank battery? What voltage are they outputting over USB-C PD? The Volts and Amp-hours (not amp/hours) metrics make sense when comparing raw battery cells, but when integrated into a device where the voltage is unknown or variable output for charging different devices, it becomes less relevant. Watt-hours tells you the total energy. A laptop with more Watt-hours has more battery than one with fewer Watt-hours, all in a single unit without needing to multiply things together.
  - ilyt 3y ago
    >Why provide watt/hours and force people to back-convert to amp/hours? Because you don't use amp-hours for ANYTHING. If you have battery and want to know how long your 3.3V device will run from it, the simplest way to do it is to just measure power your device uses and compare it with Wh of battery. Doesn't matter whether input is single 3.7V battery or 18V battery pack, all you care for is your device power usage and your power supply efficiency at that voltage. > For batteries of the same voltage, amp/hours is a simpler and easier way to compare. It's not simpler and it's exactly as easy to compare, bigger number is better...
ChrisMarshallNY 3y ago
> So we break it out into two separate, and unequally important properties for these consumers. The important property being voltage. If the voltage is the same, the battery can be considered by consumers to be "compatible" with their device. If the mAH is greater, they will have more battery life. Lower, and they will have less battery life. That's a great way of putting it. I tend to agree, but W/h can also do the same.
johntb86 3y ago
NiMH AA cells are 1.2V, while alkaline AA is 1.5V, and most devices will accept either. So for good switched power supplies Wh is more important, since that will correlate best with battery life. Of course for linear power supplies or plain resistive loads you'll get different results, so you're right that it's impossible to use a single number to summarize the capacity of a battery.
amluto 3y ago
> Consumers use batteries that are a specific voltage. Watt hours obfuscates this fact. So when a user tries to plug a 1.2v 40w/h battery into a 12v device that takes a 40 w/h battery, they will not know why it does not work. This is kind of sort of true for gadgets that take AA or AAA or maybe small lead acid batteries. They need a battery at a specific voltage (except they don’t — NiMH, carbon-zinc, alkaline, and Li (metal) batteries all tend to be interchangeable despite rather different voltages), and they consume roughly constant current. But many modern devices use fancy power supplies that consume roughly constant power. And, more relevantly to newer devices, how many consumers say “hey, that cool USB charger operates at 16V internally, so I want X mAh?” (Also, batteries have discharge curves, not constant voltages. But in mAh’s slight defense, the charge delivered from a battery is less likely to vary widely with different rates of discharge than the energy delivered.)
Joker_vD 3y ago
...your explanation would work way better if the unit dimensions actually worked out. And they don't, since W/h is not a unit of energy, and mAh is not a unit of "current per hour". And your second paragraph is bogus anyhow: the voltage would be labelled on the batteries despite whether the other metrics is charge (which is what mAh is unit of) or energy (which is what Wh is unit of). P.S. It is still beyond me why people in general don't comprehend that both "amper" and "watt" are already units of "speed", no need to divide them by time any further. Maybe we should've given km/h its own name, to ease people into such concept? /rant
- vel0city 3y ago
  Joules are a lot harder to reason about than watthours. I've got a 5W device that I run for three hours. How much energy did it use? Easy, 5W * 3 hours = 15Wh. How many joules did it use? 1 J = 1 wattsecond, so 5 * 60 * 60 * 3 = 54,000J = 54kJ.
  - Joker_vD 3y ago
    Stop dividing watts by hours or even seconds, please. 1 Joule is 1 watt sustained for 1 second, that is, 1 watt * 1 second.
    - numpad0 3y ago
      People want runtime estimates. Often for fixed voltages. There comes Ah handy. Stop complaining people do "stupid" things before even Googling what it's for.
      - vel0city 3y ago
        But Wh would be just as handy, and then wouldn't need voltages to be fixed in the comparison. For example, I've got a battery pack on my desk that says its a 10,000mAh battery pack. No additional documentation on it. It has two USB ports for output and one USB port for input. Is that mAh rated at the 5V for USB? Is that mAh rated at the probably 3.6V of the lithium pack? Is it using some other voltage internally? Is it a 36Wh battery or a 50Wh battery or something else entirely? How long is it going to run my 5W load? 10 hours? 7.2 hours? Less? That's a nearly 30% swing in runtime that I don't truly know unless I go measure it, when they could have just stamped how many Wh its good for and I'd know.
ginko 3y ago
>They know what a w/h represents as a unit of measure This is basic middle school physics..
- laszlokorte 3y ago
  And still "w/h" makes no sense. As explained in other comments watt is already "energy per time", i.e. power, i.e. "1w = 3600 J/h".
samtho 3y ago
> Consumers use batteries that are a specific voltage. Nowadays with sealed, non-serviceable batteries, it is not always abundantly clear what voltage the device takes for power (which can be different from its charging voltage) unless it’s in your hand and you can read the specifications that are printed on the back (if it is at all). Breaking out these two datapoints into voltage and amp hour no longer makes sense given that most batteries where consumer-advertised capacity are product specific. Our relationship with battery powered devices has changed since the days of 1.5V cells that we tossed in at varying amounts (2x = 3V, 4x = 6V, 6x = 9v, etc). Pre-“USB-PD”, it still kind of made sense to use mAh because we knew it was always 5v but that too has changed. The mistake is not changing to mWh once we stopped describing 5v devices.
- amluto 3y ago
  > Pre-“USB-PD”, it still kind of made sense to use mAh because we knew it was always 5v but that too has changed. Really? How many of those devices actually had 5V batteries inside? (Are there even credible 5V Li-poly battery banks?) Original USB (based on a quick search) specified 5V +- 5%. You’re not getting that by direct connection to a battery, and you also can’t charge the internal battery by direct connection to any common supply. Somewhere in the power brick is a switching converter. So maybe a 5000mAh USB-A power brick can supply 5000mAh output before conking out, but I doubt it.
  - samtho 3y ago
    > How many of those devices actually had 5V batteries inside? (Are there even credible 5V Li-poly battery banks)? That’s a good point and revealed that I conflated battery capacity with source-able/usable power. You are correct (as far as I am aware as well) that you cannot use a lithium ion/polymer based battery chemistry and have between 4.75 and 5.25 volts output. Thinking about it some more, the battery packs seem to represent a special case where the function of the device is to provide power and, as per your point about squeezing out maximum power, we probably need to have two separate power ratings: one for the battery and one for the usable output.
    - 3y ago
bryanlarsen 3y ago
> Consumers use batteries that are a specific voltage. Consumers use batteries that are a specific form factor. They don't buy 1.5V batteries, they buy AA's. They don't know or care what voltage their computer battery is, they buy a Lenovo T14 battery. Et cetera. I can't think of a common single battery where you can buy the correct form factor but get the wrong voltage. The only two pieces of information that matter are form factor and wattage. You can derive voltage from the form factor, but you can't derive form factor from voltage. You can derive amperage from wattage and voltage. Edit: I finally thought of an exception. 6V tractor batteries are form factor compatible with 12V tractor batteries. But those are hardly common in 2023.
- derbOac 3y ago
  This is maybe getting tangential but one of my pet peeves is that the industry doesn't establish standards for large batteries, like lawnmowers and leafblowers. If they were serious about electric transition they would make batteries transferable like AA, AAA batteries etc. I understand the issues involved and that there are nontrivial obstacles (see: IoT), but it is really frustrating to deal with manufacturer lock-in. I also think it adds to confusion of the sort in the linked piece because there isn't a discussion of standards per se along the lines you're mentioning. I suppose safety issues are magnified a hundredfold compared to the problems that people have run into with USB product standard mismatch but that's probably another reason why people might actually buy brand-name OEM batteries even if there were standards. I guess in general I wish there was some open industry discussion of this, even if it meant a white paper where they throw up their hands and decide it's too risky.
  - tzs 3y ago
    There is at least one company making adaptors for power tool batteries [1], so that you can do things like use your Black & Decker drill battery with your Milwaukee circular saw. They seem to be mostly around $30, but might be worth it for someone with a lot of tools with different batteries who wants to minimize the number of different chargers they have to deal with. https://powertoolsadapters.com/ https://powertoolsadapters.com/
- 3y ago
afiori 3y ago
If we need two numbers anyway why not use volts and w/h instead of volts and mAh?
jefftk 3y ago
Let's say I'm buying a portable power supply for my phone or laptop. I know my device can take a range of input voltages (for my mac: 5V, 9V, 15V, 20V, 28V; for my pixel: 5V, 9V) and know my device will negotiate with the power supply over USB-C for the correct voltage. Since my device can handle either, I would be equally happy with a power supply that used 5V internally as one that used 9V internally. So I do primarily care about the capacity of the power supply in Watt-Hours (energy).
tzs 3y ago
Since you have to specify the voltage no matter how you measure energy, because voltage is what primarily determines if a battery will work in most consumer electronics, what units you specify energy in is not relevant as far as consumers comparing batteries go. If I see that two batteries have the same stated voltage and battery A has higher mAh than B I know that A should last longer in my device. But that's exactly the same if I see A and B have the same voltage but A has higher mWh. It should last longer. Even if the energy was specified in some completely ridiculous way such as how much mass that amount of energy could lift a 2 liter bottle of diet Pepsi on the moon I'd just have to look at the two numbers and pick the bigger one.
trashtester 3y ago
By w/h, I'm sure you mean Wh, which is a unit of charge. (W/h is something completely different, and mostly relevant for how a quickly power source (like a power plant) can meet variation in power loads.) As for the rest of your explanation, it's actually NOT a good reason to label batteries by Ah or mAh over Wh. Wh is better for almost any purpose as long as it can be accurately determined. You still have to provide the voltage it is designed for, but it is just as easy to find the Ah's in a battery from the Wh as the other way around, when you know the voltage. The problem, though, is that the true voltage of a battery isn't constant, but tends to vary depending on what load you connect to it. This is because of every battery having an INTERNAL resistance (R_internal). This internal resistance will (for a basic cell) lead to a reduction of the delivered voltage (as seen by the load) by U_load = U_nominal - I*R_internal. Also R_internal can increase if the battery is cold, hot or has some defect. This means that the Ah unit provides a more precise measure for the capacity of a battery than Wh.
ikesau 3y ago
You mean W-h, right? Watt-hour, not watts-per-hour as W/h would suggest
- vel0city 3y ago
  You mean Wh right? Not watts minus hours as W-h would suggest.
  - coder543 3y ago
    > Not watts minus hours as W-h would suggest. That's not what that would suggest to most people. https://physics.nist.gov/cuu/Units/checklist.html https://physics.nist.gov/cuu/Units/checklist.html "A space or half-high dot is used to signify the multiplication of units." In practice, I'm pretty sure people often use a short dash because a half-high dot is hard to type on a keyboard. I also agree the dash is unnecessary, though.
    - vel0city 3y ago
      If the short dash means multiply, what symbol do you use for subtraction? What would the majority of people answer with this: 2-2 = ? If I put 2-2 into Google, is it going to return 0 or 4? If you're going to be pedantic, at least write it properly.
      - coder543 3y ago
        You can’t add or subtract units, so it’s not a relevant question. The dash gets used for many things. It is also used to hyphenate words, but people don’t ask how you can subtract two words. > If you're going to be pedantic, at least write it properly. I didn’t write it. I’m just explaining a commonly-used convention since you seem unfamiliar with it.
        vel0city 3y ago
        If using the - symbol was commonly meaning multiply, wouldn't Google say 4? Using - to mean multiplication is absolutely not common parlance.
soneil 3y ago
You're not wrong, but the problem we're hitting is that most mobile tech has divorced product/supply voltage from battery voltage, and the result is a lot of "white lies" where the values stated don't add up to a whole. My laptop has a 6000mAh battery and will charge from 5V. But my 10,000mAh powerbank will not fully charge it. The question is how to explain this to my mother. To calculate this properly - you have to do some actual digging to find the nominal battery voltage of the laptop, since it's not any of the USB-PD voltages, and is thus entirely divorced from the laptop's input voltage. And then you have to know that most powerbank vendors tell you the rating of the cells, not the rating of the product. So they will tell you that it's a 10,000mAh battery, and that it outputs 5V - but these two facts are only honest in isolation. It is not a 50Wh battery, it's a 37Wh battery. Or a 7,400mAh product that is powered by 10,000mAh cells. Almost anywhere we use USB-PD, stating Wh is a lot more honest to the consumer. If we tell my mother that her laptop is 70Wh and the powerbank is 37Wh, she can infer it'll give her about half a full charge. If we tell her the laptop is 6000mAh and the powerbank is 10,000mAh, she can be forgiven for inferring it'll give her almost two charges. -- For an example of what I'm calling "white lies": https://www.anker.com/products/a1271 https://www.anker.com/products/a1271 (And to be clear, I'm not blaming Anker for this, I believe it's near-universal. I'm only using Anker as an example because they're a more-trusted brand.) All the way down the bottom of the page, just above the FAQ, they give the capacity as "20100mAh/72.36Wh". 20100mAh is given 19 times - 72.36Wh is given precisely once. From 72.36Wh / 20.1Ah we get a nominal voltage of 3.6V, not 5V. 3.6V is never otherwise stated. I've never seen any vendor tell you that you're seeing the cell rating, not the product rating - but the better vendors will give you enough information to figure it out yourself.
stetrain 3y ago
If I buy a USB-C PD power bank with 10,000mAh capacity, per the USB spec it can output power at 5V, 9V, 15V, or 20V, depending on which device is plugged in. Which voltage is the 10,000mAh capacity in reference to? Most likely it's actually the internal 3.7v cell voltage, which is even less relevant than any of the potential output voltages. Your argument makes sense for purchasing raw battery cells (li-ion or plain old AAs) but as soon as those cells are integrated into a sealed consumer electronics device (battery pack, smartphone, laptop) it is no longer an interchangeable unit with a known voltage.
- adriancr 3y ago
  USB batteries de facto are considered 5V, so 10.000mah at 5V.

spookie 3y ago

Yup, that makes perfect sense

nicoburns 3y ago

There is no such thing as a device that takes a 40wh battery. A device will take a battery with a specific voltage, and will last for different amounts of time based on the capacity.

fanf2 3y ago

Your theory might make sense if the voltage was actually specified, but when I last bought a USB-C power bank I could not find that information anywhere, so I did not know if I was comparing like with like.

jfengel 3y ago
In a saner world, it would be implicit in the USB-C. As it is, you know that it supports 5V. It might also support higher voltages (up to 20V), though if it doesn't specify I wouldn't assume. If you need higher voltage, you'll have to look for a battery that specifies it. (And hope that the package isn't lying.)
- soneil 3y ago
  Every powerbank vendor I've seen gives the battery rating at 3.6/3.7V, so USB implying 5V gives us misleading values. So a 20,000mAh powerbank is 20*3.6V=72Wh, not 20*5=100Wh. I've never seen a vendor that specifies 3.6V, the best you can hope for is that they give mAh and Wh so you can derive it yourself. If we need the Wh rating to keep the mAh rating honest, the mAh becomes redundant before the Wh does.
chrisnight 3y ago
I’m not sure where you live, but I believe every battery sold in the US legally is required to label their I/O voltage and amps, and capacity voltage, amp hours, watt hours. At the very least, every wall outlet and power bank I’ve seen has text somewhere that tells what it outputs, with the powerbanks aswell having capacity, both amp hour and voltage. Though I will say the text is rather small.
- fanf2 3y ago
  The description of a typical power bank leaves voltage and watts implicit, as far as I can see https://www.amazon.com/dp/B07S829LBX/ https://www.amazon.com/dp/B07S829LBX/ I mean, I can work out what they probably are with a little general knowledge and arithmetic, but it isn’t as clear as you suggest.

throwaway894345 3y ago

> So we break it out into two separate, and unequally important properties for these consumers. The important property being voltage. If the voltage is the same, the battery can be considered by consumers to be "compatible" with their device. If the mAH is greater, they will have more battery life. Lower, and they will have less battery life. It works exactly the same way if you replace mAh with wh.

ilyt 3y ago

Devices don't say "It needs 40Wh battery" Devices say "it needs AA battery" or "It needs 18V battery" >W/H is insufficient for describing batteries unless you specify the voltage you are working with. Yes. Then do exactly that. Describe Wh and voltage.

pas 3y ago
Just describe Joules. No need to bring hours into it.
- vel0city 3y ago
  Not everyone likes to think about how many seconds their devices will last. Hours are a lot easier to reason about.
firebat45 3y ago
There are two important numbers when it comes to batteries. Volts and Amp/hours. Watt/hours is simply a calculated value. Why provide watt/hours and force people to back-convert to amp/hours? Watt-hours is only useful when comparing batteries of different voltages, which is not a very practical thing to be doing. For batteries of the same voltage, amp/hours is a simpler and easier way to compare.
- stetrain 3y ago
  What voltage is your laptop battery? Your smartphone battery? Your Anker power bank battery? What voltage are they outputting over USB-C PD? The Volts and Amp-hours (not amp/hours) metrics make sense when comparing raw battery cells, but when integrated into a device where the voltage is unknown or variable output for charging different devices, it becomes less relevant. Watt-hours tells you the total energy. A laptop with more Watt-hours has more battery than one with fewer Watt-hours, all in a single unit without needing to multiply things together.
- ilyt 3y ago
  >Why provide watt/hours and force people to back-convert to amp/hours? Because you don't use amp-hours for ANYTHING. If you have battery and want to know how long your 3.3V device will run from it, the simplest way to do it is to just measure power your device uses and compare it with Wh of battery. Doesn't matter whether input is single 3.7V battery or 18V battery pack, all you care for is your device power usage and your power supply efficiency at that voltage. > For batteries of the same voltage, amp/hours is a simpler and easier way to compare. It's not simpler and it's exactly as easy to compare, bigger number is better...

ChrisMarshallNY 3y ago

> So we break it out into two separate, and unequally important properties for these consumers. The important property being voltage. If the voltage is the same, the battery can be considered by consumers to be "compatible" with their device. If the mAH is greater, they will have more battery life. Lower, and they will have less battery life. That's a great way of putting it. I tend to agree, but W/h can also do the same.

johntb86 3y ago

NiMH AA cells are 1.2V, while alkaline AA is 1.5V, and most devices will accept either. So for good switched power supplies Wh is more important, since that will correlate best with battery life. Of course for linear power supplies or plain resistive loads you'll get different results, so you're right that it's impossible to use a single number to summarize the capacity of a battery.

amluto 3y ago

> Consumers use batteries that are a specific voltage. Watt hours obfuscates this fact. So when a user tries to plug a 1.2v 40w/h battery into a 12v device that takes a 40 w/h battery, they will not know why it does not work. This is kind of sort of true for gadgets that take AA or AAA or maybe small lead acid batteries. They need a battery at a specific voltage (except they don’t — NiMH, carbon-zinc, alkaline, and Li (metal) batteries all tend to be interchangeable despite rather different voltages), and they consume roughly constant current. But many modern devices use fancy power supplies that consume roughly constant power. And, more relevantly to newer devices, how many consumers say “hey, that cool USB charger operates at 16V internally, so I want X mAh?” (Also, batteries have discharge curves, not constant voltages. But in mAh’s slight defense, the charge delivered from a battery is less likely to vary widely with different rates of discharge than the energy delivered.)

Joker_vD 3y ago

...your explanation would work way better if the unit dimensions actually worked out. And they don't, since W/h is not a unit of energy, and mAh is not a unit of "current per hour". And your second paragraph is bogus anyhow: the voltage would be labelled on the batteries despite whether the other metrics is charge (which is what mAh is unit of) or energy (which is what Wh is unit of). P.S. It is still beyond me why people in general don't comprehend that both "amper" and "watt" are already units of "speed", no need to divide them by time any further. Maybe we should've given km/h its own name, to ease people into such concept? /rant

vel0city 3y ago
Joules are a lot harder to reason about than watthours. I've got a 5W device that I run for three hours. How much energy did it use? Easy, 5W * 3 hours = 15Wh. How many joules did it use? 1 J = 1 wattsecond, so 5 * 60 * 60 * 3 = 54,000J = 54kJ.
- Joker_vD 3y ago
  Stop dividing watts by hours or even seconds, please. 1 Joule is 1 watt sustained for 1 second, that is, 1 watt * 1 second.
  - numpad0 3y ago
    People want runtime estimates. Often for fixed voltages. There comes Ah handy. Stop complaining people do "stupid" things before even Googling what it's for.
    - vel0city 3y ago
      But Wh would be just as handy, and then wouldn't need voltages to be fixed in the comparison. For example, I've got a battery pack on my desk that says its a 10,000mAh battery pack. No additional documentation on it. It has two USB ports for output and one USB port for input. Is that mAh rated at the 5V for USB? Is that mAh rated at the probably 3.6V of the lithium pack? Is it using some other voltage internally? Is it a 36Wh battery or a 50Wh battery or something else entirely? How long is it going to run my 5W load? 10 hours? 7.2 hours? Less? That's a nearly 30% swing in runtime that I don't truly know unless I go measure it, when they could have just stamped how many Wh its good for and I'd know.

ginko 3y ago

>They know what a w/h represents as a unit of measure This is basic middle school physics..

laszlokorte 3y ago
And still "w/h" makes no sense. As explained in other comments watt is already "energy per time", i.e. power, i.e. "1w = 3600 J/h".

samtho 3y ago

> Consumers use batteries that are a specific voltage. Nowadays with sealed, non-serviceable batteries, it is not always abundantly clear what voltage the device takes for power (which can be different from its charging voltage) unless it’s in your hand and you can read the specifications that are printed on the back (if it is at all). Breaking out these two datapoints into voltage and amp hour no longer makes sense given that most batteries where consumer-advertised capacity are product specific. Our relationship with battery powered devices has changed since the days of 1.5V cells that we tossed in at varying amounts (2x = 3V, 4x = 6V, 6x = 9v, etc). Pre-“USB-PD”, it still kind of made sense to use mAh because we knew it was always 5v but that too has changed. The mistake is not changing to mWh once we stopped describing 5v devices.

amluto 3y ago
> Pre-“USB-PD”, it still kind of made sense to use mAh because we knew it was always 5v but that too has changed. Really? How many of those devices actually had 5V batteries inside? (Are there even credible 5V Li-poly battery banks?) Original USB (based on a quick search) specified 5V +- 5%. You’re not getting that by direct connection to a battery, and you also can’t charge the internal battery by direct connection to any common supply. Somewhere in the power brick is a switching converter. So maybe a 5000mAh USB-A power brick can supply 5000mAh output before conking out, but I doubt it.
- samtho 3y ago
  > How many of those devices actually had 5V batteries inside? (Are there even credible 5V Li-poly battery banks)? That’s a good point and revealed that I conflated battery capacity with source-able/usable power. You are correct (as far as I am aware as well) that you cannot use a lithium ion/polymer based battery chemistry and have between 4.75 and 5.25 volts output. Thinking about it some more, the battery packs seem to represent a special case where the function of the device is to provide power and, as per your point about squeezing out maximum power, we probably need to have two separate power ratings: one for the battery and one for the usable output.
  - 3y ago

bryanlarsen 3y ago

> Consumers use batteries that are a specific voltage. Consumers use batteries that are a specific form factor. They don't buy 1.5V batteries, they buy AA's. They don't know or care what voltage their computer battery is, they buy a Lenovo T14 battery. Et cetera. I can't think of a common single battery where you can buy the correct form factor but get the wrong voltage. The only two pieces of information that matter are form factor and wattage. You can derive voltage from the form factor, but you can't derive form factor from voltage. You can derive amperage from wattage and voltage. Edit: I finally thought of an exception. 6V tractor batteries are form factor compatible with 12V tractor batteries. But those are hardly common in 2023.

derbOac 3y ago
This is maybe getting tangential but one of my pet peeves is that the industry doesn't establish standards for large batteries, like lawnmowers and leafblowers. If they were serious about electric transition they would make batteries transferable like AA, AAA batteries etc. I understand the issues involved and that there are nontrivial obstacles (see: IoT), but it is really frustrating to deal with manufacturer lock-in. I also think it adds to confusion of the sort in the linked piece because there isn't a discussion of standards per se along the lines you're mentioning. I suppose safety issues are magnified a hundredfold compared to the problems that people have run into with USB product standard mismatch but that's probably another reason why people might actually buy brand-name OEM batteries even if there were standards. I guess in general I wish there was some open industry discussion of this, even if it meant a white paper where they throw up their hands and decide it's too risky.
- tzs 3y ago
  There is at least one company making adaptors for power tool batteries [1], so that you can do things like use your Black & Decker drill battery with your Milwaukee circular saw. They seem to be mostly around $30, but might be worth it for someone with a lot of tools with different batteries who wants to minimize the number of different chargers they have to deal with. https://powertoolsadapters.com/ https://powertoolsadapters.com/
3y ago

afiori 3y ago

If we need two numbers anyway why not use volts and w/h instead of volts and mAh?

jefftk 3y ago

Let's say I'm buying a portable power supply for my phone or laptop. I know my device can take a range of input voltages (for my mac: 5V, 9V, 15V, 20V, 28V; for my pixel: 5V, 9V) and know my device will negotiate with the power supply over USB-C for the correct voltage. Since my device can handle either, I would be equally happy with a power supply that used 5V internally as one that used 9V internally. So I do primarily care about the capacity of the power supply in Watt-Hours (energy).

tzs 3y ago

Since you have to specify the voltage no matter how you measure energy, because voltage is what primarily determines if a battery will work in most consumer electronics, what units you specify energy in is not relevant as far as consumers comparing batteries go. If I see that two batteries have the same stated voltage and battery A has higher mAh than B I know that A should last longer in my device. But that's exactly the same if I see A and B have the same voltage but A has higher mWh. It should last longer. Even if the energy was specified in some completely ridiculous way such as how much mass that amount of energy could lift a 2 liter bottle of diet Pepsi on the moon I'd just have to look at the two numbers and pick the bigger one.

trashtester 3y ago

By w/h, I'm sure you mean Wh, which is a unit of charge. (W/h is something completely different, and mostly relevant for how a quickly power source (like a power plant) can meet variation in power loads.) As for the rest of your explanation, it's actually NOT a good reason to label batteries by Ah or mAh over Wh. Wh is better for almost any purpose as long as it can be accurately determined. You still have to provide the voltage it is designed for, but it is just as easy to find the Ah's in a battery from the Wh as the other way around, when you know the voltage. The problem, though, is that the true voltage of a battery isn't constant, but tends to vary depending on what load you connect to it. This is because of every battery having an INTERNAL resistance (R_internal). This internal resistance will (for a basic cell) lead to a reduction of the delivered voltage (as seen by the load) by U_load = U_nominal - I*R_internal. Also R_internal can increase if the battery is cold, hot or has some defect. This means that the Ah unit provides a more precise measure for the capacity of a battery than Wh.

ikesau 3y ago

You mean W-h, right? Watt-hour, not watts-per-hour as W/h would suggest

vel0city 3y ago
You mean Wh right? Not watts minus hours as W-h would suggest.
- coder543 3y ago
  > Not watts minus hours as W-h would suggest. That's not what that would suggest to most people. https://physics.nist.gov/cuu/Units/checklist.html https://physics.nist.gov/cuu/Units/checklist.html "A space or half-high dot is used to signify the multiplication of units." In practice, I'm pretty sure people often use a short dash because a half-high dot is hard to type on a keyboard. I also agree the dash is unnecessary, though.
  - vel0city 3y ago
    If the short dash means multiply, what symbol do you use for subtraction? What would the majority of people answer with this: 2-2 = ? If I put 2-2 into Google, is it going to return 0 or 4? If you're going to be pedantic, at least write it properly.
    - coder543 3y ago
      You can’t add or subtract units, so it’s not a relevant question. The dash gets used for many things. It is also used to hyphenate words, but people don’t ask how you can subtract two words. > If you're going to be pedantic, at least write it properly. I didn’t write it. I’m just explaining a commonly-used convention since you seem unfamiliar with it.
      - vel0city 3y ago
        If using the - symbol was commonly meaning multiply, wouldn't Google say 4? Using - to mean multiplication is absolutely not common parlance.

soneil 3y ago

You're not wrong, but the problem we're hitting is that most mobile tech has divorced product/supply voltage from battery voltage, and the result is a lot of "white lies" where the values stated don't add up to a whole. My laptop has a 6000mAh battery and will charge from 5V. But my 10,000mAh powerbank will not fully charge it. The question is how to explain this to my mother. To calculate this properly - you have to do some actual digging to find the nominal battery voltage of the laptop, since it's not any of the USB-PD voltages, and is thus entirely divorced from the laptop's input voltage. And then you have to know that most powerbank vendors tell you the rating of the cells, not the rating of the product. So they will tell you that it's a 10,000mAh battery, and that it outputs 5V - but these two facts are only honest in isolation. It is not a 50Wh battery, it's a 37Wh battery. Or a 7,400mAh product that is powered by 10,000mAh cells. Almost anywhere we use USB-PD, stating Wh is a lot more honest to the consumer. If we tell my mother that her laptop is 70Wh and the powerbank is 37Wh, she can infer it'll give her about half a full charge. If we tell her the laptop is 6000mAh and the powerbank is 10,000mAh, she can be forgiven for inferring it'll give her almost two charges. -- For an example of what I'm calling "white lies": https://www.anker.com/products/a1271 https://www.anker.com/products/a1271 (And to be clear, I'm not blaming Anker for this, I believe it's near-universal. I'm only using Anker as an example because they're a more-trusted brand.) All the way down the bottom of the page, just above the FAQ, they give the capacity as "20100mAh/72.36Wh". 20100mAh is given 19 times - 72.36Wh is given precisely once. From 72.36Wh / 20.1Ah we get a nominal voltage of 3.6V, not 5V. 3.6V is never otherwise stated. I've never seen any vendor tell you that you're seeing the cell rating, not the product rating - but the better vendors will give you enough information to figure it out yourself.

stetrain 3y ago

If I buy a USB-C PD power bank with 10,000mAh capacity, per the USB spec it can output power at 5V, 9V, 15V, or 20V, depending on which device is plugged in. Which voltage is the 10,000mAh capacity in reference to? Most likely it's actually the internal 3.7v cell voltage, which is even less relevant than any of the potential output voltages. Your argument makes sense for purchasing raw battery cells (li-ion or plain old AAs) but as soon as those cells are integrated into a sealed consumer electronics device (battery pack, smartphone, laptop) it is no longer an interchangeable unit with a known voltage.

adriancr 3y ago
USB batteries de facto are considered 5V, so 10.000mah at 5V.