Do you use the mAh value to compare the battery capacities of different devices? This is the question I asked in our YouTube community post and with the sample size of around 500, the answer is unsurprisingly yes, the mAh value is used to compare the battery capacity of devices.
Some of you also said that you use Wh – which is the actual correct unit to gauge a battery’s capacity. Good job. Some also said that you’re using screen-on time as the battery life gauge of a phone – and that’s interesting, but we’ll talk about this later.
The world where mAh dominates
In today’s world, if we’re shopping for a phone, we’re looking at the mAh unit because that’s the only information we have regarding the battery capacity. But when we’re shopping for laptops though, it only shows the Wh value. Why do they use different units if we’re talking about the battery capacity? And which one is the correct unit to use? I mean, you already know that I’m going to say Wh but why?
Okay, I want you to just take a guess. Does this laptop have more battery capacity than this phone?
Here’s the answer. If we just look at the mAh value, then this laptop has a 4920mAh battery only – yet this phone has a 5000mAh battery. If I put the phone’s battery into this laptop, then I should get a slightly better better battery life, right? Well, that already does not make any sense. That laptop’s battery is already larger than the phone. And of course, the laptop won’t turn on.
That is because of the voltage difference. Laptops require much higher voltage compared to a phone, and that’s why their batteries are much larger than a phone’s battery despite having a similar mAh number. We’ll talk more about this later.
Introduction to Wh
If we want to know a battery’s true capacity, we also need to know its voltage. Once we incorporate the mAh value with the battery’s voltage, we get Wh. It’s just a basic multiplication of the two numbers and multiplying it by a thousand to eliminate the “mili” and we get the Wh number.
Phones come with many different types of batteries
Why we need to know its voltage is because we can’t just assume all battery supply the same voltage – even for phones. Phone A may have a different voltage than Phone S, even though both of them have the same mAh rating.
But how can we know the voltage? Unfortunately, it’s not as straightforward since phone brands do not list out the Wh value of their device’s battery. Apple doesn’t even list any values that talk about the battery capacity at all. So, we have to look at the replacement batteries instead.
For this example here, the iPhone 15 Pro Max has a 4,441mAh at 3.9V, that’s 17.32Wh in capacity. On the other hand, the Galaxy S23 Ultra is rated for 5,000mAh operating at 3.88V nominally, hence 19.40Wh.
Dual-cell batteries are misleading?
But let’s take a look at the formula once more. We can do some math magic here. Imagine that we double the voltage but half the current. It’ll still result in the same Wh value. However, the electronics will have to be designed differently.
That’s… actually exactly what’s happening to many new phones nowadays. There are a lot of phones that are using dual-cell batteries nowadays. By connecting two batteries in series, we can double the voltage but the current remains the same – and that is exactly what is happening on phones like ROG Phone series, the latest Vivo X100 series, as well as the iQOO 12. If we read the website’s footnote, it says that the mAh value is actually only half of what’s advertised. That mAh value does not reflect what we actually get.
Now, is this misleading? I don’t think so. Every phone brand that uses dual-cell batteries connected in series had to do this because people are used to the mAh measurement and not Wh. So, having an equivalent of the mAh number so people can understand the battery capacity that everyone got used to looking at. I mean imagine if ROG Phone 8 – which has an equivalent of 5,500mAh battery – is actually advertised to have 2750mAh only. Everyone will look at it and laugh but they don’t realize that they themselves are the clown.
Why laptops are using Wh
Now talk about laptops. The reason why laptops do not use mAh while listing the battery capacities is because it’s just irrelevant. Let me give you the perfect example. A gaming laptop like this has only 4,920mAh (G14) and this ASUS Zenbook 14 OLED UX3405 has a 9,702mAh battery. That means this laptop’s battery life should be nearly double the battery life… right?
Well… the comparison is not going to be that straightforward. Even though these two laptops have about the same Wh value, the voltage is completely different. Gaming laptops with power-hungry components will need higher voltage whereby lower-powered laptops use lower voltage batteries. It would be misleading to compare the laptop batteries if they have the same mAh value but completely different voltage values.
Quiz time! Let’s practice with Wh!
Okay! Now it’s time for a quiz. How many times do you think that this Ugreen power bank can charge the ROG Ally?
I’ve provided the mAh value, voltage, and also the Wh value of both devices. For this case, it’s a bit tricky and one of these values is a red herring.
If we just use the mAh value, then this Ugreen power bank is advertised to have a 25,000mAh and the ROG Ally is rated with 2,590mAh battery. If we just look at the mAh value, that means this power bank can charge the ROG Ally for more than 9 times!
But we all know that’s impossible. The Wh is the true battery capacity value. Taking a look at the information once more, the power bank has a 90Wh battery capacity whereby the ROG Ally has a 40Wh battery. That means the power bank can charge the ROG Ally for slightly more than twice, assuming 100% efficiency for some quick math, of course.
There are actually two different sets of values
Now, if you’ve been paying attention, then you might have realized there is a typical capacity and a rated capacity.
The typical capacity is the “best case scenario” but the rated capacity is the “guaranteed capacity” and has taken external factors like temperature into account.
Why SOT is misleading
Screen-on time is also a famous metric to gauge battery life but it’s quite misleading. On the surface, it is a good representation of the battery life we’re going to get. If we’re using the phone, the screen lights up – and that’s counted as “screen-on time”.
But SoT is misleading because it doesn’t tell us what background apps are running, what brightness the display is running, and what tasks are running. If we’re downloading or streaming more stuff during that usage period, then the battery is going to drain more than just reading a book on our phone, for example.
Our way of gauging battery life is more scientific as we try to eliminate as many external factors as possible, and lock it to 100 nits brightness on WiFi only before running the PCMark 10 battery life test. It’s not perfect, but we can use that result to compare battery life.
Bad updates or rogue apps – as in malicious apps – can also affect the screen-on time by having unnecessary battery drainage. That’s a topic for another day, though.
The true limit of batteries in planes
Okay, before we end this long video – I want to talk about planes and airlines. The International Air Transport Association – IATA – states that batteries below 100Wh are permitted to be on the plane.
As for why the limit is 100Wh, I can’t find any proper sources about this. How-To-Geek says “those who assess risk when setting policy feel that batteries of this size are still manageable should the worst happen.”
It seems like they just picked an easy number to go with while balancing both risk and our usage, 100Wh is the nearest “easy number” to go with.
Based on this, I can make an educated guess that they meant lithium-based batteries pose a risk of explosion and a bigger battery will pose a bigger threat with a bigger explosion. I mean, Wh is basically a different way of representing energy in Joule. 100Wh means 360,000 Joule and all of that is converted into heat while the plane is in the air – that’s not a fun thing to happen.
Remember – the Galaxy Note 7 was only using a 13.48Wh battery – 48,528 Joule of energy – and that already caused a lot of issues for everyone.
Everything wrong about this tweet
Now, let’s take a look at the facts again. According to iFixIt’s teardown of the Apple Vision Pro, they found out the AVP is actually using 3 iPhone-sized batteries stacked on top of each other, and it totals to about 46.08Wh. Each battery cell is rated for 3,969mAh – and that means 11.61V in total. Dividing that by 3, that means each battery cell is at 3.87V.
However, the battery enclosure actually only states that the Apple Vision Pro has a 35.9Wh battery – probably to enforce that 80% charge limit.
That Anker power bank though, it’s this Anker MagGo Power Bank (6.6K). Yes, the community note is wrong because it links us to the Anker 622 instead – which only has 5,000mAh. Unfortunately, the specs sheet of this power bank does not list the voltage or the watthour – and I can’t even find any teardowns of it. So, I can’t tell what’s the exact battery capacity of this power bank.
I’ll give it the benefit of the doubt that this power bank’s batteries are at 3.85V, just like the 10,000mAh version. Doing some math, that means it’s going to be 3.85V x 6.6Ah = 25.41Wh. Still lower than the Apple Vision Pro’s battery capacity, even after cutting off 20% from the true battery capacity.
Conclusion
If you made it to this part of the video, I have to say thanks once more. I really hope you enjoy this video and I enjoy doing this video too.
I do have an electronics engineering background and it just makes me mad when I see posts like this online. (dumb ass post comparing mAh)
I don’t think I have enough power to change the world to use Wh instead of mAh – but it’s a step forward. That’s why I’m asking all of you to like, subscribe, and share this video with your friends. Also, leave your comments down below.
If you do like this type of video, then let me know what other topics we should do – down in the comments section below. We’ll be talking about thermal throttling next.
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