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.
I don’t think they know about metric prefixes, Pip.
Imagine if the marketing people discovered that they could advertise that it has 19 million uWh (in Doctor Evil voice). Don’t say it too loudly though, someone at Apple might hear.
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.
Wait until you hear about µAh. This is the one secret the engineering team doesn’t want the marketing department to know.
LOL, electrons per second hour is such a cursed unit, it’s going to take some effort to make it worse.
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.
If you mean non-rechargeables, all batteries of the same technology are really the same in capacity. Doesn’t matter if you buy an expensive brand or the cheapest bulk store brand, the difference is a couple percent and depends more on the age of the cell and how it was handled.
Just get cheapest store-brand alkaline if you must, but really best avoid altogether and use rechargeable.
Alkaline batteries range from 3-5 Wh (https://docs.google.com/spreadsheets/d/16UTSIimjNXl9OP0cFWmLtISe7LHXUng_S6tyzWrjCuU/edit#gid=2136035052), Zinc batteries are around 0,6Wh
The reason phone vendors can advertise capacity is because the load (the phone) is a known quantity. They made the phone, so they can reliably estimate the battery’s capacity based on average use by that phone.
Similarly, power bank manufacturers can do the same, because the load is controlled by them. The USB port might only provide 5V at 1.5A or 3A - whatever the power bank manufacturer put in - so they can reliably estimate how much current over time the battery can provide.
But makers of alkaline batteries don’t have that knowledge. They have no way of knowing if you’re going to put them into a kid’s toy that pulls only 20mA, or a DC motor for a rotisserie that pulls 1A. So they can’t possibly provide you any measure of Ah that is going to satisfy all consumers. If they did, they’d open themselves up to legal problems for making misleading claims about their product.
I don’t find that to be a particularly compelling argument though. If you go to buy a lead acid battery for solar usage, for example, they give you the capacity based on a 20-hour discharge (or, 1/20th C rate). The same could absolutely be done for primary batteries
Lead acid self-discharges at a much, much higher rate than alkaline, though. It’s the reason alkaline batteries can live on a supermarket shelf for so long without losing any significant capacity.
Yeah, but that would require consumers do the mental math. I can see plenty of stupid complaints being made because people misunderstand the fundamental difference.
This shit should be all standardised around [micro|milli|Ø|kilo|tera]joules. mAh isn’t even energy, it’s charge!
This shit should be all standardised around [micro|milli|Ø|kilo|tera]
Agree with you there.
joules
But- would instead, suggest using watts instead of joules. In general, its quite well suited to electrical devices.
Have a 1,000w / 1kw device? Its going to draw 1,000wh of energy, or 1kw.
Although, the units are extremely similar. wh/kwh are defined as energy per hour, while a joule, is energy (in watts) per second.
Frankly I’d be fine with watt-hours too, as long as consistent. It isn’t like converting one into another is hard (1kWh = 3.6MJ).
My point for joules is twofold:
- Due to the name, plenty people confuse power (watts) with energy (watt-hours). Joules avoid this.
- You can also convert other “esoteric” units of energy to joules, for better comparison across fields. Such as “food calories” (i.e. kilocalories; 1kcal = 8.4kJ)
wh/kwh are defined as energy per hour, while a joule, is energy (in watts) per second.
It’s power times hours and power times seconds respectively. (“Per” is usually understood as division)
That said you’re right that they’re similar. The difference is only if you’re using hours or seconds to measure time.
I want my batteries energy capacity measured in calories, just in case I swallow it
