Question on how to compare batteries

[42thgamer]

Hello all

Not sure if this is the right subtopic but here we go. The past year I have bought a laptop, phone external battery and helped some others with their choice. But there's always one thing (along with many others) I don't understand. When looking for mobile devices a battery is always an important factor. The capacity is always given in mAh. I remember from my physics lessons that Wh = A x V x h. But I don't know what the V is supposed to be. Since all the devices have a different Voltage output. Is it calculated with the max V, or is there an industry standard V to calculate the Wh of a battery? Or am I on a completely on the wrong path?

Thanks in advance!

42thgamer

[mariushm]

Phone batteries are most often made out of a single cell, a lithium battery with voltage between 3v...4.2v, but the average voltage is around 3.6v

There are some phones these days that use 2 or 3 batteries in series, so they can charge the battery pack faster using 12v or 20v from a charger (quickcharge, usb type c, whatever), but the number of such phones is very rare.

 

A lithium-ion battery will have a fully charged voltage  of 4.2v  ... as energy is taken from it, the battery is discharging and the voltage decreases down to around 3v..3.2v - below this threshold, the battery can no longer provide meaningful amount of current, it's discharged.

 

A typical laptop battery will be made by several such batteries in series to obtain a higher voltage. For example, having 4 batteries in series results in a voltage of  4 x 3v ... 4 x 4.2v  = 12v...16.8v  so they can use a 18-20v laptop adapter to charge the battery (the voltage should be higher than the peak charged voltage)

 

Here's an example of a battery from an Asus laptop, which uses 3S battery : 2 batteries at a time are in parallel , then these 3 groups are connected in series to obtain the higher voltage:

 

They rate the battery pack at 10.8v , which corresponds to  10.8v / 3 = 3.6v, which is the average voltage of a lithium battery (the battery charges up to 4.2v, but will quickly discharge down to around 3.6v..3.8v and will be fully discharged at around 3v)

The individual batteries are Panasonic CGR18650CG and you can download the datasheet here : CGR18650CG-Panasonic.pdf

But if you can't or don't want to, I can tell you they're presented as nominal voltage 3.6v, and standard capacity 2250 mA. The datasheet also contains a graph showing typical discharge rates ... and you can see that at a typical 1.0lt (2150mA , the green line ) the batteries will still do around 2100 Mah and then it will go below around 3.2v. You can also see that for most of those 2100mAh, the voltage will be 3.5v +- 0.1v so the nominal voltage of 3.6v is chosen well, they're not lying.

 

So Asus decided to rate the individual batteries at  2200mAh instead of 2150mAh - probably because the average power consumption won't be as high as 1.0lt so they're confident the batteries can do closer to 2200mAh.

They take two such batteries and put them in parallel, so that's where the 4400mAh comes from: 2 batteries in parallel = 2 x current of single battery.

Then they put 3 such groups in series, and the current / capacity remains the same but voltage triples ... so 3 x 3.6v = 10.8v , 4400 mAh (or 4.4Ah)

And from these two  10.8v and 4.4Ah you get the total power of 10.8v x 4.4Ah = 47.52Wh  or 47 Wh listed on the sticker in the picture.

 

 

 

[CWALD]

different components in your laptop require different voltages which is one among many reasons your battery has more then 2 contacts. Rather then try to calculate it out, I would look up reviews with battery tests under specific loads. When you find the same test on two laptops you are comparing then you will know how long they last relative to each other, you can also preform these test on your own device to see how it compares to what you have now.

[mariushm]

Note that a lot of modern laptop batteries no longer use these round cells, but rather the big flat packs... they're still 3v..4.2v, nominal voltage 3.6v ... but they can get higher voltage batteries by stacking vertically a bunch of these .. .just stacked one on top of the other to get the higher voltages

 

example  :

 

You can see it says in the left bottom corner 11.55v  57.9Wh nominal : 5020mAh  but on the right corner they say 11.55v dc, 4795 mAh ...

so it's 3 flat pouches stacked vertically, with a 11.55 / 3 = 3.85v nominal voltage and 5020mAh standard capacity..

 

[42thgamer]

13 minutes ago, mariushm said:

 

Thanks for the good and long explanation, really informative!

Maybe i had to explain what I wanted to do a little better. I wanted to see how much I can charge my battery with an external battery. And while trying to figure that out I asked myself what it all meant.
So after reading your explanation (might have read it 2 times ), to calculate the Wh for phones I can just do the mAh x 3.6 (because that is the average).

But for laptops I have to really look at the technical details to figure out what the voltage output is?

On my external battery that I use to charge my phone, and maybe my laptop too in the future, it says that it outputs 5V. Can i use that as the voltage?

[42thgamer]

22 minutes ago, CWALD said:

different components in your laptop require different voltages which is one among many reasons your battery has more then 2 contacts. Rather then try to calculate it out, I would look up reviews with battery tests under specific loads. When you find the same test on two laptops you are comparing then you will know how long they last relative to each other, you can also preform these test on your own device to see how it compares to what you have now.

I would like to calculate how many Wh I need to charge my laptop. That's why I want to know it.

[mariushm]

It's tricky because you don't know what battery is used in the external battery pack/power bank.

I'd say a simple answer would be to assume around 20-25% more than the rating of the battery you want to charge.

 

Your laptop expects some input voltage - either 12v or 18v or the voltage it's designed for through the DC input jack, or 5v / 12v / 20v through the USB type-c connectors.

 

Your power bank uses these lithium batteries, in parallel or in series, or a mix of parallel and series.  The Wh rating of your power bank is for the RAW capacity of the battery inside, not how much power the power bank can output through its connectors.

 

Regardless of how the batteries are arranged, there has to be a dc-dc converter which converts the battery voltage to the voltage the laptop demands through the usb type c connector (if your laptop charges through usb type c)

The laptop initially detects a power supply on the other end of the usb cable, and receives the default 5v from the power bank, and the laptop then sends some commands through the usb cable telling the charger to go to 12v or 20v or whatever voltage the laptop wants.

 

This conversion is not 100% efficient - let's say if the power bank has to go from 3.2v...4.2v to 5v, it may be 95% efficient, but if it has to go from 3.2v..4.2v to 12v it may only be 90% efficient... so only 90% of the actual battery "juice" actually comes out the power bank, the other 10% is heat.

Then, your laptop has to take that 12v and charge the batteries, but that charging process again isn't 100% efficient, though it should be close to 90-95% efficient.  That's another loss.

The laptop doesn't have a clue about the source of the electricity, it assumes it's DC power, and besides heat generated charging, they're not very concerned about how efficient the charging process it.

 

 

 

[42thgamer]

3 minutes ago, mariushm said:

It's tricky because you don't know what battery is used in the external battery pack/power bank.

I'd say a simple answer would be to assume around 20-25% more than the rating of the battery you want to charge.

 

Your laptop expects some input voltage - either 12v or 18v or the voltage it's designed for through the DC input jack, or 5v / 12v / 20v through the USB type-c connectors.

 

Your power bank uses these lithium batteries, in parallel or in series, or a mix of parallel and series.  The Wh rating of your power bank is for the RAW capacity of the battery inside, not how much power the power bank can output through its connectors.

 

Regardless of how the batteries are arranged, there has to be a dc-dc converter which converts the battery voltage to the voltage the laptop demands through the usb type c connector (if your laptop charges through usb type c)

The laptop initially detects a power supply on the other end of the usb cable, and receives the default 5v from the power bank, and the laptop then sends some commands through the usb cable telling the charger to go to 12v or 20v or whatever voltage the laptop wants.

 

This conversion is not 100% efficient - let's say if the power bank has to go from 3.2v...4.2v to 5v, it may be 95% efficient, but if it has to go from 3.2v..4.2v to 12v it may only be 90% efficient... so only 90% of the actual battery "juice" actually comes out the power bank, the other 10% is heat.

Then, your laptop has to take that 12v and charge the batteries, but that charging process again isn't 100% efficient, though it should be close to 90-95% efficient.  That's another loss.

The laptop doesn't have a clue about the source of the electricity, it assumes it's DC power, and besides heat generated charging, they're not very concerned about how efficient the charging process it.

 

 

 

Okay thanks, I think I understand. Something related to this I was wondering about is the following: can i charge my laptop via usb at 5 volts and 1000 mA (so 5W)? Even if the laptop is using more than 5W? I know it wont charge the battery but it could make it so that the battery drains a little slower. Or is the pc not able to use such low power sources. I have been reading multiple posts on multiple forums and see a lot of different answers.

[mariushm]

The laptop will probably not accept that as power source and not charge or use it as extra power source.

If your laptop charges through usb type-c, it probably expects the charger on the other end to support some standards like USB Power Delivery, and with such standards, the charger has to tell the laptop what voltage and current combinations it supports, and the laptop can request a higher voltage  than 5v.

If the laptop isn't able to communicate with the charger, it will probably ignore it.

 

The laptop adapter for that HP Spectre x360 with the flat battery in the picture a few posts above can do  5v x 3A (15w) , 9v x 3A (27w) , 12v x 5A (60w) , 15v x 4.33A (65w) , 20v x 3.25A (65w).. if you charge it while using it, it will probably go to 20v ...

The current is kept low because higher currents means more losses in wires, in the usb cable..

[42thgamer]

1 minute ago, mariushm said:

The laptop will probably not accept that as power source and not charge or use it as extra power source.

If your laptop charges through usb type-c, it probably expects the charger on the other end to support some standards like USB Power Delivery, and with such standards, the charger has to tell the laptop what voltage and current combinations it supports, and the laptop can request a higher voltage  than 5v.

If the laptop isn't able to communicate with the charger, it will probably ignore it.

 

The laptop adapter for that HP Spectre x360 with the flat battery in the picture a few posts above can do  5v x 3A (15w) , 9v x 3A (27w) , 12v x 5A (60w) , 15v x 4.33A (65w) , 20v x 3.25A (65w).. if you charge it while using it, it will probably go to 20v ...

The current is kept low because higher currents means more losses in wires, in the usb cable..

Okay, so let's say the power source can only deliver 5W, than it depends on the laptop if it can use that or not?

If I connect a 5W power source via usb-c my pc says 'slow charger, use the charger that came with the charger to speed up the charging'. And if I look at the power icon it says it is on battery, but there is a yellow danger icon so something is going on. But after the battery drops under 50% it does tell me it is on a slow charger.

What do you think? Is it using the power or not? Might have to do some better testing.

 

[mariushm]

Yeah, I would say so. The exclamation icon is probably there because of the "slow charger, not using it, use a proper charger with usb power delivery standard, to set it up how I like"   ... so it says I know something is plugged in the usb port, but can't use it.

 

Your slider is another thing ... at best performance, your laptop probably consumes 40-60 watts, but at where you are with the slider (better battery, a notch less than "best battery life", the laptop probably dims the screen, aggressively throttles down the cpu cores and so on, and your laptop probably hovers around 10-20w of power consumption.

The 5w may then be used to supplement the battery and lower the discharge rate, but I doubt it.

 

To charge a battery, normally the charger has to provide more power than what it's consumed by the laptop.

[42thgamer]

2 minutes ago, mariushm said:

Yeah, I would say so. The exclamation icon is probably there because of the "slow charger, not using it, use a proper charger with usb power delivery standard, to set it up how I like"   ... so it says I know something is plugged in the usb port, but can't use it.

 

Your slider is another thing ... at best performance, your laptop probably consumes 40-60 watts, but at where you are with the slider (better battery, a notch less than "best battery life", the laptop probably dims the screen, aggressively throttles down the cpu cores and so on, and your laptop probably hovers around 10-20w of power consumption.

The 5w may then be used to supplement the battery and lower the discharge rate, but I doubt it.

 

To charge a battery, normally the charger has to provide more power than what it's consumed by the laptop.

Hmmm, interesting I will do some testing this weekend and let you know! Thanks for all the help!